3 And teaching this very thing, He said to the Jews: “Your father Abraham rejoiced that he should see my day; and he saw it, and was glad.” What is intended? “Abraham believed God, and it was imputed unto him for righteousness.” In the first place, [he believed] that He was the maker of heaven and earth, the only God; and in the next place, that He would make his seed as the stars of heaven. This is what is meant by Paul, [when he says,] “as lights in the world.” Righteously, therefore, having left his earthly kindred, he followed the Word of God, walking as a pilgrim with the Word, that he might [afterwards] have his abode with the Word.
Source: Adversus haereses (New Advent)