And when Abraham was ninety years old and nine (Gen. 17:1). Scripture says elsewhere in reference to this verse: Thou art fairer than the children of man; grace is poured upon thy lips; therefore, God hath blessed thee forever. Gird thy sword upon thy thigh, O mighty one, thy glory and thy majesty (Ps. 45:3–4). Concerning whom did Korah’s sons sing this song? They sang it about Abraham, the fairest of Adam’s descendants. Who were the descendants of Adam? They were: Seth, Cain, Mahalalel, Jared, Enoch, Methuseleth, Lamech, Noah, and his sons. Whence do we know that Noah’s sons were called the sons of Adam? It is said: And the Lord came down to see the city and the tower which the sons of Adam builded (Gen. 11:5).
Grace is poured upon thy lips alludes to the fact that you said to the king of Sodom, I will not take a shoe-latchet. Hence the Holy One, blessed be He, hath blessed you forever. Indeed, all you have done was previously known and revealed to Me: your descent into the furnace to sanctify My name; the ten trials you underwent; your pursuit after the kings; and the manner in which you were glorified. Hence, if you desire to make yourself great in this world, Gird thy sword about thy thigh (Ps. 45:4). That is, perform the circumcision between your thighs, and it will add to your majesty and your glory.
I will establish My covenant between Me and thee. He was not aware which part of his body was to be circumcised. And so the Holy One, blessed be He, indicated the place of circumcision when he said; And I will make thee exceedingly fruitful. That is to say, at the place through which you increase and multiply you are to be circumcised. However, Bar Kappara was of the opinion that Abraham decided upon the place of circumcision by analogy. He said to himself: “Which part of a tree is subject to the law of orlah? It is that part of the tree which produces fruit, and so I must be circumcised at the place from which I will produce my fruit.”