Albert Barnes Commentary 2 Chronicles 15:11

"And they sacrificed unto Jehovah in that day, of the spoil which they had brought, seven hundred oxen and seven thousand sheep." — 2 Chronicles 15:11 (ASV)

The prevalence of the number “seven” in the religious system of the Jews has been noticed often. Seven young bulls and seven rams were a common offering (Numbers 29:32; 1 Chronicles 15:26; 2 Chronicles 29:21; Job 42:8; Ezekiel 14:23). At the larger sacrifices, however, it is seldom that we find the number seven at all prominent (Compare 2 Chronicles 30:24; 2 Chronicles 35:7–9; 1 Kings 8:63).