When something is consecrated to the service of God it is said to be "holy." When we choose a building as a site for worship, we often pray and consecrate the building. We set it aside for a specific purpose: service to God. We then tend to guard it from frivolous uses.
The same thing with our bodies. We have been chosen to be vessels dedicated to God's service.
Ephesians 1:4 and
2 Peter 2:9. We are "something" that God has chosen to set aside for a specific purpose, thus we are holy by His choosing.
However, we are not inanimate objects like the vessels and instruments in the Tabernacle. We are living beings capable of making choices for ourselves as well. And so, we are exhorted to "make ourselves holy" as well.
Romans 12:1;
1 Thessalonians 4:4;
2 Timothy 2:21.