Hebrews 13:10

Believers under the Old Covenant ate part of what they offered to God as a peace offering (Leviticus 7:15-18). However believers under the New Covenant feed spiritually on Jesus Christ who is our peace offering. Those still under the Old Covenant had no right to partake of Him for spiritual sustenance and fellowship with God since their confidence was still in the Old Covenant.

"Christians had none of the visible apparatus which in those days was habitually associated with religion and worship-no sacred buildings, no altars, no sacrificing priests. Their pagan neighbors thought they had no God, and called them atheists; their Jewish neighbors too might criticize them for having no visible means of spiritual support." [Note: Bruce, The Epistle . . ., p. 400.]

Roman Catholics have tended to see in this "altar" a reference to the mass, whereas Protestants have viewed it as a reference either to Christ Himself or His cross or a heavenly altar. I prefer Christ Himself since it is through Him that we are to offer a sacrifice of praise to God (Hebrews 13:15; cf. 1 Peter 2:5).