"But he that is joined unto the Lord is one spirit." (1 Corinthians 6:17)
Our body and spirit are very closely related to one another. One cannot divide the both as one affects the other. Some try to give the body and spirit different identities that what we do in one doesn't affect the other. St. Paul clearly takes a different view here. In the writings of Paul , he often expresses the significance of body in the scheme of things in an eternal perspective. In the church at Corinth many had this view that we are free to do anything with our body because our spirit is redeemed. St. Paul destroys this argument by stating that everything is not beneficial. They said in Corinth that as the body would be destroyed, it's permissible to do it all. They indulged in gluttony and sexual immorality. St. Paul states in this passage that the body is not designed for sexual immorality but it should be used to glorify God. This body is for the Lord and the Lord resides in our body.
When we accept the Lordship of Jesus Christ, we are joined unto the Lord and we are one spirit. The Spirit of God communes deeply with our spirit and we are led by Him. This communion is for the body to carry His presence and not for us to indulge in sexual immorality. A person joined like this with the Lord should not be joined to a prostitute as they become one after the union. "Yoga" means union and we who are joined with the Lord should not be united to anything else. God will resurrect our bodies on the day of resurrection and we need to be mindful of what we do in our bodies.
For further reading: 2 Corinthians 5:10, 1 Corinthians 15:44