I believed the pre-trib position for years but I changed my view when I preached through 1 Thessalonians. There is nothing in 1 Thess. 4:13-18 about a pretribulation rapture. When Paul said, “we who are alive and remain until the coming (parousia) of the Lord, will not precede those who have fallen asleep,” he uses the word parousia meaning “coming,” “arrival,” or “presence.” There is no reason why they would not be thinking that this is the second coming in glory after the tribulation.
Yes, 1 Thes.4:13-18, which introduces the rapture doctrine in the New Testament, doesn’t indicate pre or post trib. You have to determine it’s timing from other passages like 1 Thes. 1:10, 1 Thes. 5:9, Rev 3:10, Isaiah 26:19-21, where it’s clear the Bible teaches a pre-trib rapture. But I don’t think 1 Thes. 4 can be the 2nd coming because Jesus doesn’t come to earth in a visible return in glory at the rapture but draws us up to be with Him in the air in fulfillment of John 14:1-3.
Also, at least to me, 2 Thessalonians 2 doesn’t make any sense unless Paul had taught them about a pre trib rapture of the Church. The forged letter they had written Paul about wouldn’t have upset them if it was informing them that they had missed the 2nd coming. They knew it was an event that every eye would behold, that no one could miss, and would have dismissed the letter as a fraud.
But if they thought it was telling them that they’d missed the pre-trib rapture, they’d have been scared to death for two reasons. First it would mean that they were about to experience the worst period of judgment ever to come on the world. And more importantly, it would mean that they weren’t saved and didn’t know how to become so.