Why Does St. Paul Address His Epistles “To The Saints”?

Source: vaticancatholic.com

Ephesians 1:1 — “Paul, an apostle of Jesus Christ, by the will of God, to all the saints who are at Ephesus, and to the faithful in Christ Jesus.”

Philippians 1:1 — “To all the saints in Christ Jesus who are at Philippi…”

Colossians 1:2 — “To the saints and faithful brothers in Christ at Colossae…”

1 Corinthians 1:2 — “To the church of God that is in Corinth, to those sanctified in Christ Jesus, called to be saints…”

2 Corinthians 1:1 — “To the church of God that is at Corinth, with all the saints who are in the whole of Achaia.”

The word that St. Paul uses in Ephesians 1:1, Philippians 1:1, and Colossians 1:2 is ἁγίοις.  It simply means “the sanctified ones”, referring to those who have been sanctified in baptism. 

In the same epistle St. Paul repeatedly warns the ἁγίοις (the sanctified ones) that if they commit grave sins they won’t be saved.  That refutes Protestantism.