For we walk by faith (Eidos) I have here rendered aspectum, (sight,) because few understood the meaning of the word species, (appearance.) [1] He states the reason, why it is that we are now absent from the Lord -- because we do not as yet see him face to face. (1-Corinthians 13:12.) The manner of that absence is this -- that God is not openly beheld by us. The reason why he is not seen by us is, that we walk by faith Now it is on good grounds that faith is opposed to sight, because it, perceives those things that are hid from the view of men -- because it reaches forth to future things, which do not as yet appear. For such is the condition of believers, that they resemble the dead rather than the living -- that they often seem as if they were forsaken by God -- that they always have the elements of death shut up within them. Hence they must necessarily hope against hope. (Romans 4:18.) Now the things that are hoped for are hid, as we read in Romans 8:24, and faith is the manifestation of things which do not appear. (Hebrews 11:1.) [2] It is not to be wondered, then, if the apostle says, that we have not as yet the privilege of sight, so long as we walk by faith For we see, indeed, but it is through a glass, darkly; (1-Corinthians 13:12,) that is, in place of the reality we rest upon the word.

Footnotes

1 - "Espece, ainsi qu'on a accoustumé de traduire en Latin ce mot Grec;" -- "Species, as they have been accustomed to render in Latin this Greek word." Those interpreters who have rendered eidos species, (appearance,) employ the word species to mean what is seen, as distinguished from what is invisible -- what has a visible form. The term, however, (as Calvin hints,) is ambiguous, being frequently employed to denote appearance, as distinguished from reality. -- Ed.

2 - "Concerning the import of the original term hupostasis, translated substance, (Hebrews 11:1,) there has been a good deal of discussion, and it has been understood to signify confidence or subsistence. Faith is the confidence of things hoped for; because it assures us, not only that there are such things, but that, through the power and faithfulness of God, we shall enjoy them. It is the subsistence of things hoped for; because it gives them, although future, a present subsistence in the minds of believers, so that they are influenced by them as if they were actually present. Thus the word was understood by some of the Greek commentators, who were the most competent judges of its meaning. Since things which we hope for,' says Chrysostom, seem not to subsist, faith gives them subsistence, or rather it does not give it, but is itself their substance. Thus the resurrection of the dead is not past, nor does it subsist, but faith gives it subsistence in our souls.' Faith,' says another, gives subsistence to the resurrection of the dead, and places it before our eyes...' The objects of faith are not only future good, but invisible things, both good and evil, which are made known by divine revelation; and of these it is the evidence, elenchos the demonstration or conviction... Being past, and future, and invisible on account of their distance from us, or the spirituality of their nature, they cannot be discovered by our senses, but the conviction of their reality is as strong in the mind of a believer, as if they were placed before his eyes." -- Dick's Theology, volume 3. -- Ed.

For we walk - To walk, in the Scriptures often denotes to live, to act, to conduct in a certain way; see the notes on Romans 4:12; Romans 6:4. It has reference to the fact that life is a journey, or a pilgrimage, and that the Christian is traveling to another country. The sense here is, that we conduct ourselves in our course of life with reference to the things which are unseen, and not with reference to the things which are seen.
By faith - In the belief of those things which we do not see. We believe in the existence of objects which are invisible, and we are influenced by them. To walk by faith, is to live in the confident expectation of things that are to come; in the belief of the existence of unseen realities; and suffering them to influence us as if they were seen. The people of this world are influenced by the things that are seen. They live for wealth, honor, splendor, praise, for the objects which this world can furnish, and as if there were nothing which is unseen, or as if they ought not to be influenced by the things which are unseen. The Christian, on the contrary, has a firm conviction of the reality of the glories of heaven; of the fact that the Redeemer is there; of the fact that there is a crown of glory; and he lives, and acts as if that were all real, and as if he saw it all. The simple account of faith, and of living by faith is, that we live and act as if these things were true, and suffer them to make an impression on our mind according to their real nature; see the note on Mark 16:16.
It is contradistinguished from living simply under the influence of things that are seen. God is unseen - but the Christian lives, and thinks, and acts as if there were a God, and as if he saw him. Christ is unseen now by the bodily eye; but the Christian lives and acts as if he were seen, that is, as if his eye were known to be upon us, and as if he was now exalted to heaven and was the only Saviour. The Holy Spirit is unseen; but he lives, and acts as if there were such a Spirit, and as if his influences were needful to renew, and purify the soul. Heaven is unseen; but the Christian lives, and thinks, and acts as if there were a heaven, and as if he now saw its glories. He has confidence in these, and in kindred truths, and he acts as if they were real. Could man see all these; were they visible to the naked eye as they are to the eye of faith, no one would doubt the propriety of living and acting with reference to them.
But if they exist, there is no more impropriety in acting with reference to them than if they were seen. Our seeing or not seeing them does not alter their nature or importance, and the fact that they are not seen does not make it improper to act with reference to them. There are many ways of being convinced of the existence and reality of objects besides seeing them; and it may be as rational to be influenced by the reason, the judgment, or by strong confidence, as it is to be influenced by sight. Besides, all people are influenced by things which they have not seen. They hope for objects that are future. They aspire to happiness which they have not yet beheld. They strive for honor and wealth which are unseen, and which is in the distant future. They live, and act - influenced by strong faith and hope - as if these things were attainable; and they deny themselves, and labor, and cross oceans and deserts, and breathe in pestilential air to obtain those things which they have not seen, and which to them are in the distant future.
And why should not the Christian endure like labor, and be willing to suffer in like manner, to gain the unseen crown which is incorruptible, and to acquire the unseen wealth which the moth does not corrupt? And further still, the people of this world strive for those objects which they have not beheld, without any promise or any assurance that they shall obtain them. No being able to grant them has promised them; no one has assured them that their lives shall be lengthened out to obtain them. In a moment they may be cut off and all their plans frustrated; or they may be utterly disappointed and all their plans fail; or if they gain the object, it may be unsatisfactory, and may furnish no pleasure such as they had anticipated. But not so the Christian. He has:
(1) The promise of life.
(2) he has the assurance that sudden death cannot deprive him of it. It at once removes him to the object of pursuit, not from it.
(3) he has the assurance that when obtained, it shall not disgust, or satiate, or decay, but that it shall meet all the expectations of the soul, and shall be eternal.
Not by sight - This may mean either that we are not influenced by a sight of these future glories, or that we are not influenced by the things which we see. The main idea is, that we are not influenced and governed by the sight. We are not governed and controlled by the things which we see, and we do not see those things which actually influence and control us. In both it is faith that controls us, and not sight.

For we walk by faith - While we are in the present state faith supplies the place of direct vision. In the future world we shall have sight - the utmost evidence of spiritual and eternal things; as we shall be present with them, and live in them. Here we have the testimony of God, and believe in their reality, because we cannot doubt his word. And to make this more convincing he gives us the earnest of his Spirit, which is a foretaste of glory.

(For we walk by (e) faith, not by sight:)
(e) Faith, of those things which we hope for, not having God presently in our physical view.

For we walk by faith, and not by sight. Faith is a grace which answers many useful purposes; it is the eye of the soul, by which it looks to Christ for righteousness, peace, pardon, life, and salvation; the hand by which it receives him, and the foot by which it goes to him, and walks in him as it has received him; which denotes not a single act of faith, but a continued course of believing; and is expressive, not of a weak, but of a strong steady faith of glory and happiness, and of interest in it: and it is opposed to "sight": by which is meant, not sensible communion, but the celestial vision: there is something of sight in faith; that is a seeing of the Son; and it is an evidence of things not seen, of the invisible glories of the other world; faith looks at, and has a glimpse of things not seen, which are eternal; but it is but seeing as through a glass darkly; it is not that full sight, face to face, which will be had hereafter, when faith is turned into vision.

we walk--in our Christian course here on earth.
not by sight--Greek, "not by appearance." Our life is governed by faith in our immortal hope; not by the outward specious appearance of present things [TITTMANN, Greek Synonyms of the New Testament]. Compare "apparently," the Septuagint, "by appearance," Numbers 12:8. WAHL supports English Version. 2-Corinthians 4:18 also confirms it (compare Romans 8:24; 1-Corinthians 13:12-13). God has appointed in this life faith for our great duty, and in the next, vision for our reward [SOUTH] (1-Peter 1:8).

For we cannot clearly see him in this life, wherein we walk by faith only: an evidence, indeed, that necessarily implies a kind of "seeing him who is invisible;" yet as far beneath what we shall have in eternity, as it is above that of bare, unassisted reason.