2 Thessalonians 2:13-15

But we are bound to give thanks to God always for you, brethren beloved of the Lord, for that God chose you from the beginning unto salvation in sanctification of the Spirit and belief of the truth: whereunto he called you through our gospel, to the obtaining of the glory of our Lord Jesus Christ. So then, brethren, stand fast, and hold the traditions which ye were taught, whether by word, or by epistle of ours.