Jamieson, Fausset and Brown on Numbers 20:24-28

24-28. Aaron shall be gathered unto his people--In accordance with his recent doom, he, attired in the high priest's costume, was commanded to ascend that mountain and die. But although the time of his death was hastened by the divine displeasure as a punishment for his sins, the manner of his death was arranged in tenderness of love, and to do him honor at the close of his earthly service. His ascent of the mount was to afford him a last look of the camp and a distant prospect of the promised land. The simple narrative of the solemn and impressive scene implies, though it does not describe, the pious resignation, settled faith, and inward peace of the aged pontiff.