Exodus 32:29

Offer up yourselves to the honour and service of the Lord in this work, which because it was joined with the hazard of their lives, he calls it a consecration or oblation of themselves, as Abraham for the like reason is said to have offered up Isaac. Consecrate yourselves, Heb. fill your hands, & c., i.e. offer a sacrifice, for so the phrase is oft used, as Exodus 28:41 Judges 17:5,12. That work of justice which they were going to execute might seem an inhuman and barbarous act, but he tells them it was an acceptable sacrifice to God, as the destruction of God's enemies is called a sacrifice, Isaiah 34:6 Ezekiel 39:17. Or he hereby intimates that this tribe was designed by God for his immediate service, and therefore recommends this work to them as an excellent initiation into their office, and as a demonstration that they were in some sort worthy of that great trust.