'Solemn' in the Bible

Observe, I am about to build a house for the Name of the Lord my God, dedicated to Him, to burn fragrant incense [of sweet spices] before Him, to set out the showbread continually, and to offer burnt offerings morning and evening, on Sabbaths, New Moons, and on the festivals of the Lord our God, as ordained forever in Israel.

On the eighth day they held a celebration, for they had observed the dedication of the altar for seven days, and the feast for seven days.

a certain number every day, offering them up as Moses commanded for the Sabbaths, the New Moons, and the three annual feasts—the Feast of Unleavened Bread, the Feast of Weeks, and the Feast of Booths (Tabernacles).