Augustine of Hippo, On the Grace of Christ, and on Original Sin II.32: He Shows by the Example of Abraham that the Ancient Saints Believed in the Incarnation of Christ

Chapter 32 [XXVII.]—He Shows by the Example of Abraham that the Ancient Saints Believed in the Incarnation of Christ.

For it must not be supposed that those saints of old only profited by Christ’s divinity, which was ever existent, and not also by the revelation of His humanity, which had not yet come to pass. What the Lord Jesus says, “Abraham desired to see my day, and he saw it, and was glad,” meaning by the phrase his day to understand his time, affords of course a clear testimony that Abraham was fully imbued with belief in His incarnation. It is in respect of this that He has a “time;” for His divinity exceeds all time, for it was by it that all times were created. If, however, any one supposes that the phrase in question must be understood of that eternal “day” which is limited by no morrow, and preceded by no yesterday,—in a word, of the very eternity in which He is co-eternal with the Father,—how would Abraham really desire this, unless he was aware that there was to be a future mortality belonging to Him whose eternity he wished for? Or, perhaps, some one would confine the meaning of the phrase so far as to say, that nothing else is meant in the Lord’s saying, “He desired to see my day,” than “He desired to see me,” who am the never-ending Day, or the unfailing Light, as when we mention the life of the Son, concerning which it is said in the Gospel: “So hath He given to the Son to have life in Himself.” Here the life is nothing less than Himself. So we understand the Son Himself to be the life, when He said, “I am the way, the truth, and the life;” of whom also it was said, “He is the true God, and eternal life.” Supposing, then, that Abraham desired to see this equal divinity of the Son’s with the Father, without any precognition of His coming in the flesh—as certain philosophers sought Him, who knew nothing of His flesh—can that other act of Abraham, when he orders his servant to place his hand under his thigh, and to swear by the God of heaven, be rightly understood by any one otherwise than as showing that Abraham well knew that the flesh in which the God of heaven was to come was the offspring of that very thigh?