John Piper provides these brief, yet clarifying definitions that I found helpful:
“Justification is the biblical teaching that, by grace alone through faith alone, God counts believers in Jesus Christ to be perfectly righteous and totally acceptable in his presence forever. That is, God imputes the perfection of Christ to those who are united to Christ by faith (Rom. 3:28; 4:4-6; 5:1, 18-19; 8:1; 1 Cor. 1:30; 2 Cor. 5:21; Phil. 3:8.”
“Sanctification is the biblical teaching that we are progressively conformed to the image of Christ in our attitudes and words and actions by the power of the Holy Spirit moving through faith to make us become in daily practice what we have already become in Christ (Rom. 6:22; 1 Cor. 5:7; Phil. 2:12-13; 3:12; Eph. 4:24).”
*John Piper, Think: The Life of the Mind and the Love of God (Wheaton: Crossway, 2010), 69.