Malachi uses the language of entering into a covenant as he talks about marriage. When we marry, we enter into a covenant with the person we marry and with God.  Our ultimate loyalty is to God and honoring God in how we treat our spouse.  God makes us one as husband and wife. Each of us belongs to the other, and we each belong to God: " In body and spirit, you are his," Malachi reminds us. For godliness to come from our union, each person in this covenant commits to living to show love and give honor to the other.
In a fallen and broken world, a world where Satan looks to steal, destroy, and kill relationships,  Malachi reminds us that we must firmly commit to three things:
- Each belongs to God, both in body and spirit. He is the one Who made us one in marriage, and our desire must be to please Him. How we treat each other is part of the worship we offer to Him. 
- We must guard our hearts. We must guard our hearts in a sex-crazed, sexually distorted, and sexually destructive world. Not all sin is the same, and sexual sin can leave a destructive "residue" of memories that can be destructive to our relationships in marriage. 
- We must practice loyalty to both God and our spouse in our marriage. Despite times when we are upset, angry, or broken by the other person, God wants us to be loyal to Him and our spouse because He wants to protect us from Satan. He doesn't want the evil one to gain a foothold in our relationship and destroy the gift God has given us. 
How vital are these principles that Malachi gives us? Notice how Malachi finishes his thoughts on this crucial covenant:
"For I hate divorce!" says the Lord, the God of Israel. "To divorce your wife is to overwhelm her with cruelty," says the Lord of Heaven's Armies. "So guard your heart; do not be unfaithful to your wife." 
In a world of throwaway commitments, God reminds us that our commitment isn't just with another person; it is also a covenant with Him. There are no throwaway commitments for God because there are no throwaway people!