There is no promise in the Bible that we will not suffer during the Great Tribulation. On the contrary, many believers will die during this time of Satan's wrath (Revelation 12:12). The day of the Lord will happen after the Great Tribulation.
If you do a study of the day of the Lord, you will see that:
- there are prophesied events before it
- only God will be exalted during this time
- God will punish his enemies