What did the Corinthians turn from and turn to when they came to God?

The Corinthians turned from idols to the living God. They came out of abject paganism with its immorality and idolatrous practices and began to worship the one true God. They became changed people, living epistles known and read by all men.

Les explains that the Corinthians, like the Thessalonians, had turned from idols to the living God. They had come out of abject paganism with all of its immorality and idolatrous practices, and they had begun to worship the one true God. Because of this change, the apostle could call them his epistle, written in his heart, known and read of all men. Les likes to feel the same about those who come to know the Lord through his simple teaching—they become living epistles. As the context cites, they are manifestly declared to be the epistle of Christ, ministered by us, written not with ink but with the Holy Spirit of the living God, not on tables of stone but on the heart as believers.

1 Corinthians 1:1

Paul, called to be an apostle of Jesus Christ through the will of God, and Sosthenes our brother,

See the rest

What did the Corinthians turn from before they began to worship the one true God?

The Corinthians turned from idols to the living God, coming out of abject paganism with its immorality and idolatrous practices. They left those practices behind and began to worship the one true God, becoming changed people who were living epistles.