Vine’s: “…fundamentally signifies separated (among the Greeks, dedicated to the gods), and hence, in Scripture in its moral and spiritual significance, separated from sin and therefore consecrated to God, sacred.”
Thayer: “2. Set apart for God, to be, as it were, exclusively His…”
In the New Testament a “saint” is the same as a Christian, disciple, believer, and so on. They were living, not dead, as many references show. Paul wrote to the saints in Rome (Rom. 1:7), Corinth (1 Cor. 1:2), Ephesus (Eph. 1:1), Philippi (Phil. 1:1), Colosse (Col. 1:2), and Thessalonica (1 Thes. 3:13). Saints are the ones who made up local congregations (Phil. 1:1).
To be a saint, biblically, is to be one devoted, set apart to God. It means you have committed your life to serving Jesus. This includes doing His will and teaching others to do His will.
A saint is sanctified, as 1 Corinthians 1:2 says. One is sanctified in Christ. It is by His blood that we are set apart from the world and become a child of God (Heb. 10:10). Since this is the case, we are no longer the master of our lives and bodies, rather they belong to God (1 Cor. 6:18-20; 7:23).
A saint does not live like the rest of the world. The speech and actions of a saint distinguish him or her from others. Saints do not use filthy language (Eph. 5:3, 4). They are not sexually immoral or covetous, nor are they filled with wrath or malice or lies (Col. 3:5-9). Saints are conscious of their behavior and the thoughts that lead to that behavior (Phil. 4:8).