the breach in unity

Unity is assumed but it has been breached. From the International Standard Bible Encyclopedia:

In both Old Testament and New Testament the assumption of unity between God and man stands over against the contrasted fact that there is a radical breach in this unity. This breach is recognized in all God’s relations to men; and even when healed it is always subject to new failures which must be provided for, by the daily oblations in the Old Testament, by the continuous intercession of the Christ (Hebrews 7:25; 9:24) in the New Testament. Even when there is no conscious breach, man is taught to recognize that it may exist and he must avail himself of the appointed means for its healing, e.g. daily sacrifices. This breach is universally attributed to some behavior on man’s part. This may be moral or ceremonial uncleanness on man’s part. He may have broken with God fundamentally in character or conduct and so by committing sin have incurred guilt; or he may have neglected the fitting recognition that his life is in common with God and so by his disregard have incurred uncleanness. After the first breach between God and man it is always necessary that man shall approach God on the assumption that this breach needs healing, and so always come with an offering. In human nature the sin breach is rooted and universal (Romans 3:9-19; 5:12-14).