Now may the God of peace Himself sanctify you completely; and may your whole spirit, soul, and body be preserved blameless at the coming of our Lord Jesus Christ. He who calls you is faithful, who also will do it.
1 Thessalonians 5:23-24
This is a great passage for those of us who become discouraged with our spiritual progress. We're beset with temptations, interruptions, adjustments, weaknesses, and relapses. It's often two steps forward and one step backward.
Recommended Reading:
1 Thessalonians 5: 16 – 28
If that's the way you feel today, study these verses and notice: (1) God is the One who will sanctify you and cause you to mature into the image of Christ. Yes, it takes work on your part, which is detailed in the book of First Thessalonians. But God is the source and strength of our progress. (2) One day you'll be completely whole, perfect, and pleasing to God in every way. (3) This will happen at the Second Coming of our Lord Jesus Christ. (4) Until then, we're works in progress—and it involves our whole spirit, soul, and body.
He has called you, and He will be faithful to work in you what is pleasing to Him.