Why did Paul the Apostle compare humans to temples of God?

When a person accepts Jesus Christ as their personal Savior (Born Again; Saved; Regenerated; come to the Lord, a Christian) the Holy Spirit comes to dwell in that person.

The Holy Spirit is "God the Holy Spirit", the third person of the Trinity.

I Corinthians 3:16-17, " Do you not know that you are the temple of God and that the Spirit of God dwells in you? If anyone defiles the temple of God, God will destroy him. For the temple of God is holy, which temple you are."

I Corinthians 6:19-20, "Or do you not know that your body is the temple of the Holy Spirit who is in you, whom you have from God, and you are not your own? For you were bought with a price; therefore glorify God in your body and in your spirit, which are God's."

The Christian's body is a temple because the Holy Spirit dwells with in them. We belong to God.