4 he who opposes and exalts himself against all that is called God or that is worshiped, so that he sits as God in the temple of God, setting himself up as God. WEB
“he who opposes” (he) The antichrist will go against the Lord and force people to redirect their worship of God to himself.
“exalts himself against all that is called God” Since the beginning, Satan wanted to be exalted to God’s position as seen in the Book of Isaiah…
12 How you have fallen from heaven, shining one, son of the dawn! How you are cut down to the ground, who laid the nations low! 13 You said in your heart, “I will ascend into heaven! I will exalt my throne above the stars of God! I will sit on the mountain of assembly, in the far north! 14 I will ascend above the heights of the clouds! I will make myself like the Most High!”
The antichrist [the beast] of Revelation will take over the world through force [wars], deceptions, and by controlling its economy [the mark of the beast].
“he sits as God in the temple of God, setting himself up as God.” For the antichrist to sit in God’s temple refers to a third temple that needs to be built before this event takes place.
Once the third temple is constructed, he will stop the Jewish people from sacrificing in it and will sit behind the veil [the holy of holies] to pronounce to the world that he is indeed God. In Matthew 24:15-16, Jesus said that when you see his [the antichrist] image [Revelation 13:14-15] on the corner of the third temple, run for the mountains to save your lives. That is when he breaks the peace treaty with Israel and forces them to receive his mark and worship only him or face death.