Matthew 3:1-12 presents John the Baptist preaching repentance. He came to prepare the way of the Lord. John the Baptist baptized in water for repentance. He prophesied that Jesus would baptize in the Holy Spirit and fire. John the Baptist is still under the law but prepares the way for Jesus.
In stark contrast to the New Testament gospel Exodus 21 and Exodus 22 contain regulations on servanthood and slavery, penalties for manslaughter and personal injuries, all Mosaic law.
John the Baptist was a transition figure. He still preached repentance to return to full obedience of the Mosaic law. Bot he also prepared the way of the Lord. He proclaimed that Jesus would baptize in the Holy Spirit and fire, giving new life, as Jesus would later explain. For now, Jesus also preached repentance and promised the Kingdom of heaven was near.
I for one is thankful we are no longer under Mosaic law, but under God’s perfect law; Follow the Lord Jesus Christ, love one another, pray continually, rejoice always, in everything give thanks etc.