And Isaac prayed to the LORD for his wife: Revised Standard Version follows the Hebrew clause order, which gives the action taken before the reason. This will be natural in some languages, but others will prefer to place the reason clause first. Prayed translates a verb that occurs only this one time in Genesis. It is found also in Exo 10.18 and is always a request or plea directed to God. For discussion of “pray” see 20.7. For LORD see 2.4 and “The names of God in Genesis,” in “Translating Genesis,” page 13. For his wife must often be expressed as “prayed that the LORD would heal his wife.”

Because she was barren gives the reason for Isaac’s prayer. Barren translates the same word used of Sarah’s condition in 11.30. It now becomes apparent that Isaac, like his father, must depend upon God to intervene to keep the promise he made to Abraham in 12.2.

A suggested rendering of verse 21 is, for example, “Rebekah was unable to have children, and so Isaac prayed to the LORD for her” or “Because Rebekah could not become pregnant, Isaac asked the LORD to give her children.” See also Good News Translation.

And the LORD granted his prayer: granted his prayer translates a passive form of the Hebrew verb “pray” used in the first part of this verse and which has the literal sense “he was prayed to” and means “he [the LORD] answered the prayer.” That is, “The LORD did what Isaac asked him to do.”

And Rebekah his wife conceived: that is, she became pregnant.

Quoted with permission from Reyburn, William D. and Fry, Euan McG. A Handbook on Genesis. (UBS Helps for Translators). New York: UBS, 1997. For this and other handbooks for translators see here .