21. to build an altar unto the Lord, that the plague may be stayed—It is evident that the plague was not stayed till after the altar was built, and the sacrifice offered, so that what is related (2Sa 24:16) was by anticipation. Previous to the offering of this sacrifice, he had seen the destroying angel as well as offered the intercessory prayer (2Sa 24:17). This was a sacrifice of expiation; and the reason why he was allowed to offer it on Mount Moriah was partly in gracious consideration to his fear of repairing to Gibeon (1Ch 21:29, 30), and partly in anticipation of the removal of the tabernacle and the erection of the temple there (2Ch 3:1).