The Catechism in Questions & Answers

673. What happens at the dedication of a church building?

A church building is dedicated on the occasion of the first divine service conducted there. In the dedication prayer, the house of God is dedicated as the place where the Holy Spirit reveals Himself—that is, the place where God’s word is proclaimed and the sacraments are dispensed—in the name of the triune God.
The dedicated church is a place for the worship of God and a sanctuary for those who seek salvation. It is here that divine grace and comfort, strength of faith, and peace of the soul are offered in the divine services.