Read 1 Thessalonians 2:16 Using Other Translations
Forbidding us to speak to the Gentiles that they might be saved, to fill up their sins alway: for the wrath is come upon them to the uttermost.
by hindering us from speaking to the Gentiles that they might be saved--so as always to fill up the measure of their sins. But God's wrath has come upon them at last!
as they try to keep us from preaching the Good News of salvation to the Gentiles. By doing this, they continue to pile up their sins. But the anger of God has caught up with them at last.