For it was not through [obedience to] law [See 3:31] that the promise to Abraham or his descendants of inheriting [the best of] the world [was made], but through their being considered righteous because of faith [in God].

For if [only] those who are obedient to the law deserve an inheritance, [then their] faith [in God] is for nothing, and God's promise is nullified.

For this reason, the promise [i.e., of being made right with God] comes through faith [in God], according to His unearned favor, so that it may be [given] with certainty to all of Abraham's descendants. The promise is given not only to those [who live] under the law [i.e., the Jews], but also to [all] those [who live] by faith, like Abraham. Abraham is the [spiritual] father of all of us [believers],

just as it is written [Gen. 17:5], "I [i.e., God] have made you [i.e., Abraham] forefather of many nations." He received this promise in the presence of God, in whom he believed, and who gives life [back] to dead people and who refers to things [promised] as though they were [already] fulfilled.

Yet he looked for the promise of God [to be fulfilled] and did not waver, doubting [that it would happen], but his faith strengthened him. He honored God

But it is not as if the word of God [i.e., His promise to Israel] has failed [in its fulfillment]. For not all those descended from the Israelites are [truly] Israelites [i.e., God's people].

This means that it is not the physical descendants [of Abraham] who are God's children, but it is the children [born] according to [God's] promise who are [Abraham's true] descendants.

For these are the words of the promise [Gen. 18:10], "I [i.e., God] will come at the appointed time and Sarah will have a son."