What a glorious day!

It was my first time witnessing the dedication of a Catholic church, and the place was filled with dozens of parish priests from across the diocese. I don’t think I’ve ever seen that many priests gathered in one place outside of Rome.

The dedication of churches or altars is the responsibility of the bishop.

The Mass was celebrated by the Bishop. It was a long ceremony that lasted for four hours, which included a procession from the old church to the new and the gathering outside the doors of the new church. The bishop greets all present and addresses the people using the text:

O God, sanctifier and ruler of your Church, it is right for us to celebrate your name in joyful proclamation; for today your faithful people desire to dedicate to you, solemnly and for all time, this house of prayer, where they worship you devoutly, are instructed by the word, and are nourished by the Sacraments. adoremus.org

After the procession reached the sanctuary, a vessel of water was brought to the bishop for him to bless. He then walked through the church, sprinkling the walls and the people. When he returned to the sanctuary, he sprinkled the altar, which was still bare and undecorated.

The celebration continued with the singing Gloria!

After the Bishop's homily and we recited the Creed. After which, the bishop invites the assembly to join in the singing of the Litany of Saints. This was followed by the placement of the relics of a saint beneath the altar.

Once this has been done, the bishop then intones or says the long Prayer of Dedication. This prayer is rich with scriptural imagery and allusions to the Paschal Mystery which will be remembered and celebrated for years to come in this new building and upon the new altar. adoremus.org

Then the Bishop wears an apron.

The bishop anoints the bare altar, pouring Holy Chrism in the center and on all four corners. The fragrance of the chrism fills the whole church!

The anointing of the altar renders the altar itself as a powerful symbol of Christ, which means “Anointed One,” who on the altar of his body offered the sacrifice of his life for the salvation of all.adoremus.org

The decons wipe down the altar, then a brazier for the burning of incense is then placed on the altar.

bra·zier (/ˈbrāZHər/) - a portable heater consisting of a pan or stand for holding lighted coals.

The bishop places incense on the hot coals in the brazier, or he lights the mound of incense set directly on the altar. As the incense burns, he fills several thuribles and uses one of them to incense the altar. After that, ministers move through the church, incensing the people and even the walls.

A thurible (or censer) is a metal vessel, usually on chains, used to burn incense during religious ceremonies to create fragrant smoke, symbolizing prayers rising to heaven, purification, and reverence for God, the altar, and the congregation, uniting earthly worship with heavenly worship. It's used in Christianity (Catholic, Orthodox, Anglican) and some other traditions for solemn occasions like Mass, funerals, and blessings, honoring sacred people, objects, and moments.
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As the rite’s Introduction indicates (n. 16b), the incense burned on the altar actually signifies the sacrifice of Christ “ascending to God as a pleasing fragrance.” It is also a sign of the prayers of the people rising up to the throne of God. “Moreover,” the Instruction continues, “the incensation of the main body of the church indicates that the dedication makes it a house of prayer; but the People of God are incensed first, for they are the living temple in which each faithful member is a spiritual altar.” adoremus.org

After this powerful and fragrant moment, the altar is finally covered with its proper linens. It now stands as the Lord’s table, ready for the offering and set with the care you’d give to a festive celebration!

Then the bishop directs the altar candles and those throughout the church to be lighted with these words (70): “Let the light of Christ shine brightly in the Church, that all nations may attain the fullness of truth.” This new building and its altar have been blessed with water, dedicated to liturgical service, anointed with Chrism, and further blessed with large amounts of incense. The Word of God has already resounded within its walls for the first time. Now the light of Christ at last illuminates this space, forever set aside as a particular community’s place of worship.
adoremus.org

And the bishop now approaches the newly dedicated altar and kisses it for the first time.

This very short article can only scratch the surface of the rich symbolism, strong prayer, and joyful celebration that come with dedicating a church. Many of the world’s oldest buildings still in use are churches, so for most people, seeing a new one dedicated is something they may only experience once.