פירוש על בראשית 22:16

BECAUSE THOU HAST DONE THIS THING. In the beginning He promised him that he would increase his descendants as the stars of heaven³⁸⁷Above, 15:5. and the dust of the earth,³⁸⁸Above, 13:16. but now He gave him the additional assurance that because thou hast done this great deed, He swore by His Great Name [that He would increase his descendants as the stars of heaven, and as the sand which is upon the seashore],³⁸⁹Verse 17 here. and that his seed will possess the gate of its enemies.³⁸⁹Verse 17 here. Thus Abraham was assured that no sin whatever would cause the destruction of his descendants, nor would they fall into the hand of their enemies and not rise again. Thus this constitutes a perfect Divine assurance of the redemption which is destined to come to us.

Because you have done this thing, etc.: From that which it said, "and you did not withhold your son," we understand from this that the statement, "because you have done," is another matter. Moreover [an explanation is required], since above (Genesis 22:12), it said, "and you did not withhold your only son from Me" - whereas here it did not say, "from Me." And also the doubling of the expression, "I will surely bless you," requires an answer. As, according to Rashi's answer - [that] one is for the father and one is for the son - the duplication of, "I will surely multiply," is problematic. Hence it appears to me that with every [part of the] divine service, he said, "May it be His will that it is as if my son were slaughtered," etc. Hence it is as if he did two deeds. For he did the sacrifice of the ram in actual practice, and the sacrifice of his son in thought. Hence it is stated, "because you have done this thing" - meaning, the doing of the sacrificing; since all of the promises were said to him in the merit of the sacrifices. And, "and you did not withhold your only son," is due to his mentioning him with each [part of the] divine service. That is why it did not state, "from Me," which indicates actual sacrificing. For at this point, he did not consider actually sacrificing him. Hence, "I will surely bless you," is a double blessing - one corresponding to the act and one corresponding to the thought. And that is [also] the reason for, "I will surely multiply."

ויאמר בי נשבעתי, G’d added an oath to the blessing He had already bestowed on Avraham. When G’d swears an “oath” it is as if He were to say “by My life, etc.” Just as He is eternal and therefore will be able to keep His oath, so He can keep His oath to the children and grandchildren of the ones to whom He promises something by oath. While it is true that G’d does not need to swear an oath to assure us that He will keep His word, the new element in G’d swearing an oath is that even if the recipient of the oath did not keep his part of the bargain, i.e. sinned in the meantime, G’d promises that this will not invalidate His blessing, the one He confirms by an oath. Furthermore, He added another dimension to the existing blessing,