Charles Ellicott Commentary Leviticus 12:1

"And Jehovah spake unto Moses, saying," — Leviticus 12:1 (ASV)

And the Lord spoke to Moses. — As the reason why God graciously addressed the regulation about the clean and unclean animals to Moses and Aaron conjointly no longer operates here, the Lord now addresses the laws of purification to the Lawgiver alone.

The laws of defilement contracted from outside by eating or coming in contact with unclean objects are naturally followed by precepts about defilement arising from within the human body itself.

The spiritual guides in the time of Christ, however, account for the sequence of these laws by declaring that the arrangement follows the order of the Creation. Just as at the Creation God made the animals first, and then formed man, so in the laws of purity the animals take precedence over man and are treated first.