Exodus 20:25

And if thou wilt make Me an altar of stone, if the children of Israel should prefer such an altar, thou shalt not build it of hewn stone; for it thou lift up thy tool upon it, thou hast polluted it, literally: for thy sharpness thou swingest above it, and thou desecratest It. Ornamentation of the altar of the Lord under the circumstances in which the Israelites found themselves would have redounded to their own glory, and not to that of the Lord.