Christians are those who have accepted the invitation of the gospel of Christ.  It is by the gospel that God calls people to become a part of His kingdom.

2 Thessalonians 2:13-14 (ESV)
¹³  But we ought always to give thanks to God for you, brothers beloved by the Lord, because God chose you as the firstfruits to be saved, through sanctification by the Spirit and belief in the truth. ¹⁴  To this he called you through our gospel, so that you may obtain the glory of our Lord Jesus Christ.

While the gospel is the power of God unto salvation (Romans 1:16), we should take note of why we were called in the first place.  While we were called to be saved (ver. 13), Paul gives us another reason in Romans 1:7.

Romans 1:7 (KJV)
⁷  To all that be in Rome, beloved of God, called to be saints: Grace to you and peace from God our Father, and the Lord Jesus Christ.

We were called to be saints.  The question is what is a saint?  The Greek word for saint is hagios and means, among other things, to be set apart.  We get the word holy from the same Greek word.  So, to be a saint is to live a sanctified life, holy and separated from sin.  Paul emphasized the importance of this separation when he wrote to the brethren at Corinth.  He taught them, and by necessary inference, he teaches us, not to be unequally yoked together with unbelievers (2 Corinthians 6:14-18).  Notice, especially, what he wrote in ver. 17.

2 Corinthians 6:17 (ESV)
¹⁷  Therefore go out from their midst, and be separate from them, says the Lord, and touch no unclean thing; then I will welcome you,

This is what it means to be a saint—to live a life separated from the unrighteous standard of the world.  Paul’s instruction to touch no unclean thing points to the holiness with which we are to live.  He stresses this further at the beginning of the next chapter.

2 Corinthians 7:1 (ESV)
¹  Since we have these promises, beloved, let us cleanse ourselves from every defilement of body and spirit, bringing holiness to completion in the fear of God.

How do we bring holiness to completion?  We do so by living according to the high standard of the gospel of Christ, refraining from the allurements of the world.

Romans 12:2 (ESV)
²  Do not be conformed to this world, but be transformed by the renewal of your mind, that by testing you may discern what is the will of God, what is good and acceptable and perfect.

This holy living, which is the essential part of being a saint, begins with the heart, or what Paul refers to as “the renewal of your mind.”  The renewed mind is the one that is determined to please God and refrain from willful sin.  This is what we have been called to do.

All of this reminds us that we must be saints, not just in name, but in deed.  We do not have to act like the world.  We do not have to go along with prevailing customs of the world just because it is the popular thing to do.  We must be different.  That is what being a saint really means.   The saint aims to please God, not man, and his actions are going to reflect this.

God said, “You shall be holy for I am holy” (1 Peter 1:16).  This is our calling.  It is what we have been called to be—saints.  Paul exhorts us to walk in a manner worthy of this calling (Ephesians 4:1).

As you wind down for the night, think about these things.