And be ye kind one to another. With bitterness he contrasts kindness, or gentleness of countenance, language, and manners. And as this virtue will never reign in us, unless attended by compassion, (oumpatheia,) he recommends to us to be tender-hearted This will lead us not only to sympathize with the distresses of our brethren, as if they were our own, but to cultivate that true humanity which is affected by everything that happens to them, in the same manner as if we were in their situation. The contrary of this is the cruelty of those iron-hearted, barbarous men, by whom the sufferings of others are beheld without any concern whatever. Forgiving one another. The Greek word here rendered forgiving, (charizomenoi heautois,) is supposed by to mean beneficence. Erasmus, accordingly, renders it (largientes) bountiful. Though the word admits of that meaning, yet the context induces me to prefer the other view, that we should be ready to forgive It may sometimes happen, that men are kind and tender-hearted, and yet, when they receive improper treatment, do not so easily forgive injuries. That those whose kindness of heart in other respects disposes them to acts of humanity, may not fail in their duty through the ingratitude of men, he exhorts them to discover a readiness to lay aside resentment. To give his exhortation the greater weight, he holds out the example of God, who has forgiven to us, through Christ, far more than any mortal man can forgive to his brethren. [1]

Footnotes

1 - See Calvin's Commentary on Philippians, Colossians, etc., [9]page 213.

And be ye kind one to another - Benignant, mild, courteous, "polite" - χρηστοὶ chrēstoi. 1-Peter 3:8. Christianity produces true courteousness, or politeness. It does not make one rough, crabby, or sour; nor does it dispose its followers to violate the proper rules of social contact. The secret of true politeness is "benevolence," or a desire to make others happy; and a Christian should be the most polite of people. There is no religion in a sour, misanthropic temper; none in rudeness, stiffness, and repulsiveness; none in violating the rules of good breeding. There is a hollow-hearted politeness, indeed, which the Christian is not to aim at or copy. His politeness is to be based on "kindness;" Colossians 3:12. His courtesy is to be the result of love, good-will, and a desire of the happiness of all others; and this will prompt to the kind of conduct that will render his conversation. with others agreeable and profitable.
Tender-hearted - Having a heart disposed to pity and compassion, and especially disposed to show kindness to the faults of erring brethren; for so the connection demands.
Forgiving one another - see the notes on Matthew 6:12.
As God for Christ's sake hath forgiven you - As God, on account of what Christ has suffered and done, has pardoned you. He has done it:
(1) "freely" - without merit on your part - when we were confessedly in the wrong.
(2) "fully;" he has forgiven "every" offence.
(3) "Liberally;" he has forgiven "many" offences, for our sins have been innumerable.
This is to be the rule which we are to observe in forgiving others. We are to do it "freely, fully, liberally." The forgiveness is to be entire, cordial, constant. We are not to "rake up" old offences, and charge them again upon them; we are to treat them as though they had not offended, for so God treats us Learn:
(1) That the forgiveness of an offending brother is a duty which we are not at liberty to neglect.
(2) the peace and happiness of the church depend on it. All are liable to offend their brethren, as all are liable to offend God; all need forgiveness of one another, as we all need it of God.
(3) there is no danger of carrying it too far. Let the rule be observed, "As God has forgiven you, so do you forgive others." Let a man recollect his own sins and follies; let him look over his life, and see how often he has offended God; let him remember that all has been forgiven; and then, fresh with this feeling, let him go and meet an offending brother, and say, "My brother, I forgive you. I do it frankly, fully, wholly. So Christ has forgiven me; so I forgive you. The offence shall be no more remembered. It shall not be referred to in our contact to harrow up your feelings; it shall not diminish my love for you; it shall not prevent my uniting with you in doing good. Christ treats me, a poor sinner, as a friend; and so I will treat you."

Be ye kind one to another - Γινεσθε - χρηστοι· Be kind and obliging to each other; study good breeding and gentleness of manners. A Christian cannot be a savage, and he need not be a boor. Never put any person to needless pain.
Tender-hearted - Ευσπλαγχνοι· Compassionate; having the bowels easily moved (as the word implies) to commiserate the state of the wretched and distressed.
Forgiving one another - Should you receive any injury from a brother, or from any man, be as ready to forgive him, on his repentance and acknowledgment, as God was, for Christ's sake, to forgive you when you repented of your sins, and took refuge in his mercy.
1. The exhortations given in this chapter, if properly attended to, have the most direct tendency to secure the peace of the individual, the comfort of every family, and the welfare and unity of every Christian society. That God never prohibits any thing that is useful to us, is an unshaken truth. And that he never commands what has not the most pointed relation to our present and eternal welfare, is not less so. How is it, then, that we do not glory in his commandments and rejoice in his prohibitions? If the gratification of our fleshly propensities could do us good, that gratification had never been forbidden. God plants thorns in the way that would lead us to death and perdition.
2. From the provision which God has made for the soul's salvation, we may see the nature, and in some sense the extent, of the salvation provided. Much on this subject has been said in the preceding chapter, and the same subject is continued here. God requires that the Church shall be holy, so that it may be a proper habitation for himself; and he requires that each believer should be holy, and that he should, under the influences of his grace, arrive at the measure of the stature of the fullness of Christ! Ephesians 4:13. This is astonishing; but God is able to make all grace abound towards us.
3. It is the will of God that Christians should be well instructed; that they should become wise and intelligent; and have their understandings well cultivated and improved. Sound learning is of great worth, even in religion; the wisest and best instructed Christians are the most steady, and may be the most useful. If a man be a child in knowledge, he is likely to be tossed to and fro, and carried about with every wind of doctrine; and often lies at the mercy of interested, designing men: the more knowledge he has, the more safe is his state. If our circumstances be such that we have few means of improvement, we should turn them to the best account. "Partial knowledge is better than total ignorance; he who cannot get all he may wish, must take heed to acquire all that he can." If total ignorance be a bad and dangerous thing, every degree of knowledge lessens both the evil and the danger. It must never be forgotten that the Holy Scriptures themselves are capable of making men wise unto salvation, if read and studied with faith in Christ.
4. Union among the followers of Christ is strongly recommended. How can spiritual brethren fall out by the way? Have they not all one Father, all one Head? Do they not form one body, and are they not all members of each other? Would it not be monstrous to see the nails pulling out the eyes, the hands tearing off the flesh from the body, the teeth biting out the tongue, etc., etc.? And is it less so to see the members of a Christian society bite and devour each other, till they are consumed one of another? Every member of the mystical body of Christ should labor for the comfort and edification of the whole, and the honor of the Head. He that would live a quiet life, and keep the unity of the Spirit in the bond of peace, must be as backward to take offense as to give it. Would all act on this plan (and surely it is as rational as it is Christian) we should soon have glory to God in the highest, and on earth peace and good will among men.
5. A roughness of manners is to some unavoidable; it is partly owing to the peculiar texture of their mind, and partly to their education. But there are others who glory in, and endeavor to cultivate, this ungentle disposition; under this is often concealed a great degree of spiritual pride, and perhaps some malignity; for they think that this roughness gives them a right to say grating, harsh, and severe things. They should be taught another lesson; and if they will not demean themselves as they ought, they should be left to themselves, and no man should associate with them. They are not Christians, and they act beneath the character of men.

And be ye kind one to another, tenderhearted, forgiving one another, (19) even as God for Christ's sake hath forgiven you.
(19) An argument taken from the example of Christ, most grave and strong, both for the pardoning of those injuries which have been done to us by our greatest enemies, and much more for having consideration of the miserable, and using moderation and gentle behaviour towards all men.

And be ye kind one to another,.... Good, affable, courteous; which appears in looks, words, and actions; by looking pleasantly on each other, speaking kindly to one another, and mutually doing every good office that lies in their way, and in their power:
tender hearted: which is opposed to a being hard hearted to them that are in distress, and close at hand to the needy; to cruelty and severity to such who are subject to them, or have injured them; and to a rigid and censorious spirit to them that are fallen:
forgiving one another, even as God for Christ's sake hath forgiven you; whatever offences are given, or injuries done by the saints one to another, and so far as they are committed against them, they should forgive, and should pray to God for one another, that he would manifest his forgiveness of them, as committed against him; and this should be done in like manner as God forgives in Christ, and for his sake; that is, fully and freely, and from their hearts; and so as to forget the offences, and not to upbraid them with them hereafter; yea, they should forgive them before they repent, and without asking for it, and that for Christ's sake, and because they are members of his: the Complutensian edition reads, "even as Christ hath forgiven us": the Arabic version also reads us, and so some copies: the words may be rendered, "giving freely to one another, even as God in Christ has given freely to you"; saints should give freely to one another, for outward support, where it is needful; and should impart spiritual gifts and experience for inward comfort, where it is wanted, and as they have ability; and that from this consideration, that all they have, whether in temporals or spirituals, is freely given by God in Christ, and for his sake; with whom he freely gives them all things; in whom he has given them grace, and blessed them with all spiritual blessings; as peace, pardon, righteousness, and eternal life.

(Luke 7:42; Colossians 3:12).
even as--God hath shown Himself "kind, tender-hearted, and forgiving to you"; it is but just that you in turn shall be so to your fellow men, who have not erred against you in the degree that you have erred against God (Matthew 18:33).
God for Christ's sake--rather as Greek, "God in Christ" (2-Corinthians 5:19). It is in Christ that God vouchsafes forgiveness to us. It cost God the death of His Son, as man, to forgive us. It costs us nothing to forgive our fellow man.
hath forgiven--rather as Greek, "forgave you." God has, once for all, forgiven sin in Christ, as a past historical fact.

As God, showing himself kind and tenderhearted in the highest degree, hath forgiven you.