When will the Jewish remnant that survived the tribulation believe in Christ?
The Jewish remnant preserved through the tribulation will believe in Christ when He returns visibly and establishes His Kingdom. Seeing Him come in the clouds of glory, they will trust Him instantly—in a moment—so that the nation is born spiritually in a day, and the New Covenant becomes reality.
Les explains that this passage describes the New Covenant, which God will make with the house of Israel after those days. It will not be Israel's own choice; that company of Jews will not simply decide to follow God. Instead, when Christ returns and sets up His Kingdom, the remnant He has kept through the tribulation period will see Him coming in the clouds of glory. They will believe in a moment. Les points to Isaiah 66, saying the nation will be born in a moment, and that all Israel will be born in a day spiritually. Then the New Covenant becomes a reality, and God puts His Word and commandments in their hearts. Paul deals with this remnant in Romans 9, 10, and 11.