What had the Corinthians turned away from and turned to before Paul wrote to them?

Before Paul wrote to them, the Corinthians had turned from idols to the living God. They had come out of abject paganism, with its immorality and idolatrous practices, and had begun to worship the one true God. Their changed lives served as a living epistle.

Les explains that these 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 all of its idolatrous practices, and they had begun to worship the one true God. He says their changed lives were an epistle, written in our hearts, known and read of all men, living epistles with the Holy Spirit's work written on the heart.

1 Corinthians 1:1

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

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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.