Sanctification or Holiness, the act of God's grace whereby we are made holy, is the second definite work and is subsequent to salvation. (John 17:15-21; Hebrews 13:12)
The word sanctify means "to make holy, purify, consecrate, dedicate, cleanse, and separate." In order to be sanctified, the born-again Christian must consecrate, dedicate, and separate himself to God and His will. Then God will do His part by purifying the heart and making it holy.
After being sanctified, the Christian has a heart that is perfect toward God, though he is still subject to the limitations due to his humanity and thus not immune to the possibility of errors in judgment or imperfections due to human frailty. Spiritual growth occurs as the sanctified person continues to apply God's Word to his heart, and strives to walk daily in God's will.
Luke 1:74-75; John 17:15-17; 2 Corinthians 7:1; Ephesians 5:25-27; Hebrews 2:11; 12:14; 13:12; 1 Peter 1:16; 1 John 1:7