romans 4:17 (As it is written, I have made thee a father of many nations,) before him whom he believed, even God, who quickeneth the dead, and calleth those things which be not as though they were. - Free Bible Online

      17. As it is written, &c.-- (Ge 17:5). This is quoted to justify his calling Abraham the "father of us all," and is to be viewed as a parenthesis.
      before--that is, "in the reckoning of."
      him whom he believed--that is, "Thus Abraham, in the reckoning of Him whom he believed, is the father of us all, in order that all may be assured, that doing as he did, they shall be treated as he was."
      even God, quickeneth the dead--The nature and greatness of that faith of Abraham which we are to copy is here strikingly described. What he was required to believe being above nature, his faith had to fasten upon God's power to surmount physical incapacity, and call into being what did not then exist. But God having made the promise, Abraham believed Him in spite of those obstacles. This is still further illustrated in what follows.

JFB.