For God. — This gives the reason for stating that the Lord will take vengeance on such sins; because they are not part of the terms on which His Father called us. It should be “did not call.” These 1 Thessalonians 4:7-8, sum up the little disquisition, returning to the principle announced in 1 Thessalonians 4:3.
Unto uncleanness, but unto holiness. — The preposition translated “unto” has the same force in Galatians 5:13, “Called unto liberty,” and Ephesians 2:10, “Created unto good works.” It implies not so much the definite end to which we are invited, as the terms on which the invitation will still stand; for the call is not yet accomplished. (See Note on 1 Thessalonians 2:12.) The second “unto” in the Greek is simply “in,” used in the same sense as in 1 Thessalonians 4:4. Paraphrase, “For God did not call us on the understanding that we might be unclean, but by the way of sanctification.”
Holiness is a mistranslation for sanctification. The process, not the quality, is meant.