A saint is a person who believes in Jesus and belongs to God. The word "saint" means "holy one" or "someone set apart for God."
The Old Testament believers were called to be “holy,” or set apart for God (Exodus 22:31; Leviticus 11:44). In the New Testament, “saints” became the apostle Paul's favorite name for Christians (Romans 1:7; 8:27; 12:13; 15:25–26, 31; 16:2, 15; plus 31 other places in Paul’s letters). The name is also used 14 times in the book of Revelation. Other New Testament writers used it sometimes (Hebrews 6:10; 13:24; Jude 1:3).
Being called a saint means that Christians should live holy lives (Hebrews 12:10; Revelation 22:11). God has chosen them to be his special people, like priests who serve him. They should live differently from people who do not follow God (1 Peter 1:15–16; 2:5, 9). More than that, they are the people of the coming age, who will rule with God over the earth and angels.