Matthew Poole and continuators on Genesis 25:21

21 And Isaac intreated the LORD for his wife, because she was barren: and the LORD was intreated of him, and Rebekah his wife conceived.

He prayed, as the Hebrew word signifies, instantly or fervently, frequently and continually, for near twenty years together, for so long it was between their marriage and the first child: He was so much concerned because not onely his comfort, but the truth of Gods promise, depended upon this mercy: And he knew very well, that Gods purpose and promise did not exclude, but require, the use of all convenient means for their accomplishment.

Or, in the presence of his Wife, signifying, that, besides their more secret devotions, they did ofttimes in a more solemn manner, and with united force pray for this mercy wherein they were both equally concerned. Or, over against his wife, noting that each of them did severally and apart intreat God for this mercy, so that there was a concurrence, if not in place, yet in design and action.

As diverse of those holy women that were progenitours of Christ have long been, that it might appear that that sacred stock was propagated more by the vertue of Gods grace and promise, then by the power of nature.

Marginal references: Rom. 9. 10.