Why does Paul talk about grace so often in his letters?

Paul frequently speaks of grace because it was one of his favorite words and he continually referred to the grace of God. Grace reveals that God is not merely a demanding lawgiver; even the vilest sinner remains the object of God's love and attention because of His grace.

Les explains that grace must have been one of Paul's favorite words, since he is always referring to the grace of God. In verse 3 Paul writes, "Grace be unto you and peace from God our Father and from the Lord Jesus Christ," and in verse 4 he thanks God for the grace given to the Corinthians by Jesus Christ. Les emphasizes that very few professing Christians truly comprehend the grace of God; most assume God is still a demanding lawgiver who brings trouble if people fail His commands. That is not grace. Grace means even the vilest sinner is still the object of God's love and attention.

1 Corinthians 1:3

Grace be unto you, and peace, from God our Father, and from the Lord Jesus Christ.

What was one of Paul's favorite words in his letters?

Grace was one of Paul's favorite words. In his letters he continually refers to the grace of God, as shown in the greeting “Grace be unto you” and in his thanksgiving for the grace of God given to believers by Jesus Christ. This theme appears repeatedly.