II Thessalonians 2:13-15

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