Let us not be weary in well-doing. Well-doing (kalon) does not simply mean doing our duty, but the performance of acts of kindness, and has a reference to men. We are instructed not to be weary in assisting our neighbours, in performing good offices, and in exercising generosity. This precept is highly necessary; for we are naturally reluctant to discharge the duties of brotherly love, and many unpleasant occurrences arise by which the ardor of the best disposed persons is apt to be cooled. We meet with many unworthy and many ungrateful persons. The vast number of necessitous cases overwhelms us, and the applications which crowd upon us from every quarter exhaust our patience. Our warmth is abated by the coolness of other men. In short, the world presents innumerable hinderances, which tend to lead us aside from the right path. Most properly, therefore, does Paul admonish us not to relax through weariness. If we faint not. That is, we shall reap the fruit which God promises, if we "persevere to the end." (Matthew 10:22.) Those who do not persevere resemble indolent husbandmen, who, after ploughing and sowing, leave the work unfinished, and neglect to take the necessary precautions for protecting the seed from being devoured by birds, or scorched by the sun, or destroyed by cold. It is to no purpose that we begin to do good, if we do not press forward to the goal. In due season [1] Let no man, from a wish to gather the fruit in this life, or before its proper time, deprive himself of the spiritual harvest. The desires of believers must be both supported and restrained by the exercise of hope and patience.

Footnotes

1 - 'Egenesan amphoteroi kata tous idious kairous turannoi Surakouson. "Both at their onwn time became tyrants of Syracuse" -- Polybius. Xenophon and other classical writers employ the phrase en kairo in the general sense of "seasonably," and sometimes very nearly in the same sense as when the adjective idios is added. Kur. Paid.. 8:5. 5. -- Ed

And let us not be weary in welldoing - See the note at 1-Corinthians 15:58. The reference here is particularly to the support of the ministers of religion Galatians 6:6, but the apostle makes the exhortation general. Christians sometimes become weary. There is so much opposition to the best plans for doing good; there is so much to be done; there are so many calls on their time and their charities; and there is often so much ingratitude among those whom they endeavor to benefit, that they become disheartened. Such Paul addresses, and exhorts them not to give over, but to persevere.
For in due season - At the day of judgment. Then we shall receive the full reward of all our self-denials and charities.
We shall reap, if we faint not - If we do not give over, exhausted and disheartened. It is implied here, that unless a man perseveres in doing good to the end of life, he can hope for no reward. He who becomes disheartened, and who gives over his efforts; he that is appalled by obstacles, and that faints on account of the embarrassments thrown in his way; he that pines for ease, and withdraws from the field of benevolence, shows that he has no true attachment to the cause, and that his heart has never been truly in the work of religion. He who becomes a true Christian, becomes such for eternity. He has enlisted, never to withdraw. He becomes pledged to do good and to serve God always. No obstacles are to deter, no embarrassments are to drive him from the field. With the vigor of his youth, and the wisdom and influence of his riper years; with his remaining powers when enfeebled by age; with the last pulsation of life here, and with his immortal energies in a higher world, he is to do good. For that he is to live. In that he is to die; and when he awakes in the resurrection with renovated powers, he is to awake to an everlasting service of doing good, as far as he may have opportunity, in the kingdom of God.

Let us not be weary - Well-doing is easier in itself than ill-doing; and the danger of growing weary in the former arises only from the opposition to good in our own nature, or the outward hinderances we may meet with from a gainsaying and persecuting world.
In due season we shall reap - As the husbandman, in ploughing, sowing, and variously laboring in his fields, is supported by the hope of a plentiful harvest, which he cannot expect before the right and appointed time; so every follower of God may be persuaded that he shall not be permitted to pray, weep, deny himself, and live in a conformity to his Maker's will, without reaping the fruit of it in eternal glory. And although no man obtains glory because he has prayed, etc., yet none can expect glory who do not seek it in this way. This is sowing to the Spirit; and the Spirit and the grace are furnished by Christ Jesus, and by him the kingdom of heaven is opened to all believers; but only those who believe, love, and obey, shall enter into it.

(7) And let us not be weary in well doing: for in due season we shall reap, if we faint not.
(7) Against those who are generous at the beginning, but do not continue, because the harvest seems to be deferred a long time, as though the seed time and the harvest were simultaneous.

And let us not be weary in well doing,.... This may be understood of well doing, or doing good works in general, of every sort; which are such as are done according to the will of God, from a principle of love to him, in faith, and in the name and strength of Christ, and with a view to the glory of God: or else acts of beneficence to Christ's ministers and poor in particular; which are agreeable to the mind of God, and wellpleasing in his sight: and in doing which men should not be weary; nor are they, when their spiritual strength is renewed, and grace is in exercise, though they may meet with many things which tend to discourage and make them weary; such as change in their own circumstances, losses in the world, the multitude of objects, the ungratefulness of some, and unworthiness of others:
for in due time we shall reap; either in this world, sooner or later; in proper time, in God's own time, by enjoying an increase of the fruits of righteousness; for the seed sown shall spring up again; the bread that is cast on the waters will be found after many days; and such as honour the Lord with their substance shall be blessed with plenty of temporal good things, either they or theirs: or else in the other world, or at the end of this; which will be the harvest time, the reaping time, the time of enjoying eternal life:
if we faint not; but continue to the end, persevere constantly in doing acts of beneficence, and patiently wait, as the husbandman does, for the precious fruits of the earth; for there must be a distance of time between sowing and reaping; men must not expect to reap as soon as they sow; and therefore should not be weary of sowing, nor impatient in waiting, though they do not see as yet the appearance of the fruits thereof; for in their season they will be seen and enjoyed.

(2-Thessalonians 3:13). And when we do good, let us also persevere in it without fainting.
in due season--in its own proper season, God's own time (1-Timothy 6:15).
faint not--literally, "be relaxed." Stronger than "be not weary." Weary of well-doing refers to the will; "faint not" to relaxation of the powers [BENGEL]. No one should faint, as in an earthly harvest sometimes happens.

But let us not be weary in well doing - Let us persevere in sowing to the Spirit. For in due season - When the harvest is come, we shall reap, if we faint not.