The Elect does not necessarily refer to Christians. In the Old Testament the Jews are called the elect on several occasions, for example. Isaiah 45:4 “For Jacob my servant's sake, and Israel mine elect, I have even called thee by thy name: I have surnamed thee, though thou hast not known me.”
Through out history the nation of Israel is at the center of God's plan. Time and time again in the old testament we see a pattern repeated God blesses Israel, Israel turns their back on God, God judges Israel, and Israel turns back to God and the cycle repeats. The time of Jacobs trouble is God's end to this cycle. He will give the devil a free hand and let his judgment poor out on the world for their wickedness. As always God saves a remnanment, the 144,000 who are sealed (elect). The purpose of the tribulation is to turn the hearts of Israel to her Messiah and then he will restore them permanently to a place of blessing.
Ezekiel 39 describes the outcome v22-26 “So the house of Israel shall know that I am the Lord their God from that day and forward. And the heathen shall know that the house of Israel went into captivity for their iniquity: because they trespassed against me, therefore hid I my face from them, and gave them into the hand of their enemies: so fell they all by the sword. According to their uncleanness and according to their transgressions have I done unto them, and hid my face from them. Therefore thus saith the Lord God; Now will I bring again the captivity of Jacob, and have mercy upon the whole house of Israel, and will be jealous for my holy name; After that they have borne their shame, and all their trespasses whereby they have trespassed against me, when they dwelt safely in their land, and none made them afraid.”
The elect in the new testament are gentiles and Jews, here in 1 Thess 4 it is referring to all in Christ at that time.