The poet William Stafford wrote about the spirit of reverence in which he describes this human imperative: "A great event is coming, bow down." He reflects, "And I, always looking for something anyway, / always bow down" (Things That Happen, 1970). Folks like Stafford with a highly cultivated sense of reverence know there's never a wrong time to bow, because every moment is a miracle. But it's also good to know what folks may be bowing to as they maneuver around the sacred space of Catholic churches.

First and foremost there's the altar, officially called the Table of the Lord. Because Catholic worship is centered on the celebration of the Eucharist, this table is the most important piece of furniture in the church. When entering a church it's appropriate to make a bow of the head and shoulders toward the altar. That is an act of faith in the presence of Christ in the Eucharist.

The bow itself is an ancient symbol of surrender to a higher authority: baring the back of the neck made you vulnerable to the person before whom you subjected yourself. Bowing toward the altar whenever you cross in front of it is proper. (But if you're cleaning or decorating the church or otherwise crossing frequently, the protocol is naturally suspended.)

Later in church history it became common to reserve some part of the Eucharist in a receptacle known as the tabernacle. The tabernacle is placed variously around churches, from directly above the altar (from the days when the altar was against the wall of the sanctuary) to the present practice of reserving the Eucharist at the side of the sanctuary space or sometimes in a separate chapel entirely.

Because the tabernacle contains the consecrated Body of Christ, it—like the Table of the Lord—are reverenced with a bow or even a genuflection (going down on one knee and making the Sign of the Cross over yourself). When the tabernacle is in line with the altar or shares the same sanctuary space, it is not necessary to reverence both. The proper bow is always primarily toward the Table of the Lord. Of course you'll see folks bow toward images of Jesus, his mother Mary, favorite saints, or the cross. These are devotional gestures and not obligatory. Inside the church reverencing the altar is sufficient.

Scripture
Exodus 3:4-6; Leviticus 19:30; 26:2; Psalm 86:9; Revelation 4:6-11

Books
Stories That Could Be True: New and Collected Poems by William Stafford (Harper & Row, 1982)
The Spiritual Life: Recognizing the Holy by Robert Fabing (Paulist Press, 2004)
The Holy Way: Practices for a Simple Life by Paula Huston (Loyola Press, 2003)