Couldn't God just protect believers during the Tribulation? Is it really necessary to remove them from the earth?
Yes, the Lord could provide believers with supernatural protection. In fact, He will do precisely that when He provides saints who are present in the Tribulation with protection from the stings of the demonic locust attack that will be part of the trumpet judgments (Revelation 9:4).
But God's promise to the Church during the Tribulation is not one of protection, but one of deliverance. Jesus said that when the signs pointing to the Tribulation "begin to take place," believers are to look up because their "redemption is drawing near" (Luke 21:28). He also urged believers to pray that they might "escape all these things" (Luke 21:36).
There really is no purpose for the Church to be present during the Tribulation. It is a time of the pouring out of God's wrath upon those who have rejected His grace, love and mercy.
There are some who argue that the Church must be "purged" during the Tribulation to purify it. But to me, this idea is absurd. The blood of Jesus is sufficient to cleanse us of all our sins. That is an accomplished fact for those who have put their faith in Jesus (Ephesians 5:26-27). Furthermore, the concept of purging the Church during the Tribulation converts the whole period into a Protestant version of purgatory. It also violates the wedding imagery that the Bible uses to describe the relationship between Christ and His Church. Jesus is not going to beat up His Bride for seven years and then marry her!
Some who believe that the Church will go through the Tribulation often point to the example of Noah and his family. They were left on the earth as God poured out His wrath, but they were protected by the Lord. But this example ignores the fact that Enoch was raptured out of the world before the flood began (Genesis 5:24). I believe Enoch is a symbolic type of the Church and Noah and his family are a type of the Jewish remnant that will be protected through the Tribulation until the day that the Messiah returns.