Jamieson, Fausset & Brown

if we would judge ourselves--Most of the oldest manuscripts, read "But," not "For." Translate also literally "If we duly judged ourselves, we should not be (or not have been) judged," that is, we should escape (or have escaped) our present judgments. In order to duly judge or "discern [appreciate] the Lord's body," we need to "duly judge ourselves." A prescient warning against the dogma of priestly absolution after full confession, as the necessary preliminary to receiving the Lord's Supper.