3 What is meant by the words, “Because I live, you shall live also”? Why did He speak in the present tense of His own living, and in the future of theirs, but just by way of promise that the life also of the resurrection-body, as it preceded in His own case, would certainly follow in theirs? And as His own resurrection was in the immediate future, He put the word in the present tense to signify its speedy approach: but of theirs, as delayed till the end of the world, He said not, you live; but, “you shall live.” With elegance and brevity, therefore, by means of two words, one of them in the present tense and the other in the future, He gave the promise of two resurrections, to wit, His own in the immediate future, and ours as yet to come in the end of the world. “Because I live,” He says, “you shall live also:” because He lives, therefore shall we live also. For as by man is death, by man also is the resurrection of the dead. For as in Adam all die, even so in Christ shall all be made alive. As it is only through the former that every one is liable to death, it is only through Christ that any one can attain unto life. Because we did not live, we are dead; because He lived, we shall live also. We were dead to Him, when we lived to ourselves; but, because He died in our behalf, He lives both for Himself and for us. For, because He lives, we shall live also. For while we were able of ourselves to attain unto death, it is not of ourselves also that life can come into our possession.
4. “In that day,” He says, “you shall know that I am in my Father, and you in me, and I in you.” In what day, but in that whereof He said, “You shall live also”? For then will it be that we can see what we believe. For even now is He in us, and we in Him: this we believe now, but then shall we also know it; although what we know even now by faith, we shall know then by actual vision. For as long as we are in the body, as it now is, to wit, corruptible, and encumbering to the soul, we live at a distance from the Lord; for we walk by faith, not by sight. Then accordingly it will be by sight, for we shall see Him as He is. For if Christ were not even now in us, the apostle would not say, “And if Christ be in you, the body is dead indeed because of sin; but the spirit is life because of righteousness.” But that we are also in Him even then, He makes sufficiently clear, when He says, “I am the vine, you are the branches.” Accordingly in that day, when we shall be living the life, whereby death shall be swallowed up, we shall know that He is in the Father, and we in Him, and He in us; for then shall be completed that very state which is already in the present begun by Him, that He should be in us, and we in Him.
5. “He that has my commmandments,” He adds, “and keeps them, he it is that loves me.” He that has [them] in his memory, and keeps them in his life; who has them orally, and keeps them morally; who has them in the ear, and keeps them in deed; or who has them in deed, and keeps them by perseverance;— “he it is,” He says, “that loves me.” By works is love made manifest as no fruitless application of a name. “And he that loves me,” He says, “shall be loved of my Father, and I will love him, and will manifest myself to him.” But what is this, “I will love”? Is it as if He were then only to love, and loves not at present? Surely not. For how could the Father love us apart from the Son, or the Son apart from the Father? Working as They do inseparably, how can They love apart? But He said, “I will love him,” in reference to that which follows, “and I will manifest myself to him.” “I will love, and will manifest;” that is, I will love to the very extent of manifesting. For this has been the present aim of His love, that we may believe, and keep hold of the commandment of faith; but then His love will have this for its object, that we may see, and get that very sight as the reward of our faith: for we also love now, by believing in that which we shall see hereafter; but then shall we love in the sight of that which now we believe.
Source: Tractates on the Gospel of John (New Advent)