Here are some tremendous words from Calvin on the sheer grace of God lavished upon Abram the pagan idolater from Ur of the Chaldeans:
This calling of Abram is a signal instance of the gratuitous mercy of God. Had Abram been beforehand with God by any merit of works? Had Abram come to him, or conciliated his favour? Nay, we must ever recall to mind that he was plunged in the filth of idolatry; and God freely stretches forth his hand to bring back the wanderer. He deigns to open his sacred mouth, that he may show to one, deceived by Satan’s wiles, the way of salvation.
But this is done designedly, in order that the manifestation of the grace of God might become the more conspicuous in his person. For he is an example of the vocation of us all; for in him we perceive, that, by the mere mercy of God, those things that are not are raised from nothing, in order that they may begin to be something.
John Calvin, Genesis, (Banner of Truth), p. 343
(HT: Martin Downes)