Gen 21:1

“'וה' פקד את שרה וגו AND THE LORD VISITED SARAH —It (Scripture) places this section after the preceding one to teach you that whoever prays for mercy on behalf of another when he himself also is in need of that very thing for which he prays on the other’s behalf, will himself first receive a favorable response from God, for it is said (at end of last chapter), “And Abraham prayed for Abimelech and his wife and they brought forth” and immediately afterwards it states here, “And the Lord remembered Sarah” — i. e. he had already remembered her before he healed Abimelech (Bava Kamma 92a). פקד את שרה כאשר אמר HE REMEMBERED SARAH AS HE SAID — He remembered her by granting her pregnancy. כאשר דבר [HE DID TO SARAH] AS HE HAD SPOKEN — by granting her the birth of a son (Pesikta). Where are the expressions “saying ״ and “speaking” used respectively in regard to these? “Saying” is mentioned in the verse (17:19) “And God said (ויאמר): “nay, but Sarah, thy wife” etc.; — “Speaking“ is mentioned in (15:1) “And the word (דבר “speaking”) of the Lord came to Abraham”, and this was when He made the Covenant between the Pieces where it was stated, “This man (Eliezer) shall not be thine heir, [but one who shall be born from thee shall be thine heir],” and He brought forth this heir from Sarah. ויעש ה' לשרה כאשר דבר AND THE LORD DID UNTO SARAH AS HE HAD SPOKEN — means, spoken to Abraham.”

“AND THE ETERNAL ‘PAKAD’ (VISITED) SARAH AS HE HAD SAID. That is, by granting her pregnancy. And the Eternal did unto Sarah as He had spoken by granting her the birth of a son..Thus the words of Rashi. But the word pekidah is only an expression of remembrance and attention to the one who is remembered, such as: G-d will surely remember (‘pakod yiphkod’) you; I have surely remembered you; And Samson remembered his wife by [bringing her] a kid. Here, too, the sense of the verse is that the Eternal remembered Sarah, and He did to her as He had spoken. This expression is also found in connection with all barren women who later give birth. Thus, in the case of Rachel: And G-d remembered Rachel; and in the case of Hannah: And G-d remembered her. Similarly, the Rabb is said, “Biblical verses which mention pikdonoth are equivalent to verses which mention Divine remembrances.” is treated as one mentioning remembrance. Thus, Ramban proves that the word pakad in the verse here can mean “remembered,” and not as Rashi explained it as meaning “granting pregnancy.””

“Conjugal chastity accords with the written law by reason of the divine miracle, according to that passage of Genesis 21: The Lord visited Sarah, as He had promised, and fulfilled what He had spoken, and she conceived and bore a son in her old age, at the time which God had foretold to her. Since therefore the Lord as a benefit promised that He would give offspring to Abraham through the way of marriage, and miraculously made fruitful the dead womb of Sarah, and also gave laws according to which marriage is to be contracted: it is evident that conjugal chastity accords with the written law.”