Paul assured his readers that they were part of the intent of the gospel. God had not called them to apostleship as God had called him ( Romans 1:1), but to sainthood, saint being a common term for believer in the New Testament. It refers more to position than condition when used this way, though the implication of holiness is strong. We are primarily saints even though we sin. [1][source]
"God"s call is not an invitation but a powerful and effective reaching out to claim individuals for himself." [2][source]Romans 1:7 really continues the thought of Romans 1:1,Romans 1:2-6 being somewhat parenthetical. "Grace" and "peace" were common salutations in Greek and Jewish letters respectively in Paul"s day. God"s grace is both His unmerited favor and His divine enablement. It is the basis for any true human peace. The Hebrew concept of peace (Heb. shalom) did not just mean freedom from stress, anxiety, and irritation. It included the fullness of God"s blessing. Paul desired a continually deeper and richer experience of spiritual blessing for his readers. The linking of "Jesus Christ" with the "Father" implies the deity of the Son. [3][source]
The salutation reveals the germ ideas that the writer proceeded to develop later. This feature is also characteristic of Paul"s other epistles. So far Paul said he had a message that was in harmony with the Old Testament. It was from the risen Christ, and it was for all people. Furthermore it should lead people to obey God by exercising faith in Him. [source][source][source]