Deuteronomy 4:4 But ye that did cleave unto the Lord your God are alive every one of you this day.
Moab recalls the incident in Moab with Baal-Peor. The Lord destroyed the men that followed Baal-peor. But everyone who cleaved unto the Lord has remained alive to this day. They have avoided the death judgment of God. To cleave to is to be joined to, stuck to, glued to, held fast to, united with, and faithful to; in other words, in NT terms, to believe in Jesus. “Whosoever believes in Him shall not perish, but have eternal life.” “Whoever has the Son has life.”
Adultery was involved in the idolatry of Baal worship. The picture of faithfulness to the Lord is seen in the marriage covenant vows. “A man shall leave his father and his mother and cleave unto (hold fast to) his wife [Genesis 2:24].” Faithful marriage is an image of our relationship with our Bridegroom, Jesus.
Faithfulness to Jesus responds to His faithfulness to us. Our faithful response of faith is not derived from our fleshly efforts at commitment, but faith is given as a gift by the Holy Spirit through the Gospel. Believing is cleaving. The result is life, being alive to God and dead to sin.