Exodus 32:29

29.For Moses had said, consecrate yourselves today It is obvious that this verse was added exegetically, to give the reason why this unintimidated ardor impelled the Levites manfully to fulfill their charge, viz., because the exhortation of Moses carried them over every obstacle. The verb, “had said,” must be therefore construed in the pluperfect tense. The translation of some, (349) “ye have consecrated your hands,” in the perfect tense, is very unsuitable, since the promise is immediately added as a means of stimulating them to greater alacrity; whence it appears that the command of Moses, which has been mentioned, is now repeated in different words. They are, however, increased in forcibleness, since he declares that it will be a sacrifice sweet and acceptable to God, if, in forgetfulness of flesh and blood, they avenge the polluted worship of God. The causal particle, (350) ci, is introduced, which I have rendered nempe, (namely,) as being here an intensitive, as if he had said, such submission to God must here be shewn, that they should not even restrain their hand if necessary from their very sons and brothers. What, therefore, was lately spoken as to their relatives generally, and here of their sons, must be taken as if in the potential mood; for, if all the Levites had joined themselves with Moses, what need was there of bidding them execute punishment on their brothers or sons? So that Moses only wished to condemn that absurd regard to humanity whereby judges are often blinded, and, to the detriment of religion, are cruelly merciful in tolerating and encouraging impiety. First, therefore, let us learn from this passage, that when judges overlook crimes, their hands are defiled by their very remissness, because impunity increases licentiousness in sin. Thus Solomon teaches that,

“He that justifieth the wicked, and he that condemneth the just, even they both are an abomination to the Lord.”
(Proverbs 17:15.)

Let us also learn that nothing is less consistent than to punish heavily the crimes whereby mortals are injured, whilst we connive at the impious errors or sacrilegious (351) modes of worship whereby the majesty of God is violated.