"Has not the Lord made them one? In flesh and spirit they are his. And why one? Because he was seeking godly offspring. So guard yourself in your spirit, and do not break faith with the wife of your youth." NIV translation
God chose a specific group of women for His men to marry (be made one). They were God's possession in "flesh and spirit" and so He had the right to choose who to join together. He also gives us a reason for joining them together and not with someone else and that was to produce "godly offspring". He then tells them and us as well to "guard yourself in your spirit" (listen to Him) to find the one He would have us marry (be made one). God then goes so far as to tell them that, if they marry someone else, they will "break faith with the wife of your youth". If we remember that God knows every hair of our head (Matt. 10:30) and that He created good works for us to do before we were even born (Ephesians 2:10), we can understand what He means by "wife of your youth". God has created a specific man and woman to be married (made into one) from the time before they were even born and to marry someone else is to "break faith with the "wife of your youth".
"'I hate divorce,' says the Lord God of Israel, 'and I hate a man's covering himself with violence as well as with his garment,' says the Lord Almighty. So guard yourself in your spirit, and do not break faith." NIV translation
This verse is often used improperly as we quote the first part "I hate divorce" and forget the second part. God has always hated divorce but He also says here that He hates it when the marriage is a love/hate relationship (covering himself with violence as well as with his garment). A better translation of this is "covering his wife". God did not create the marriage relationship to be a battle ground, in fact, it was designed to make the two complete. Finally, God is telling us to not marry just anyone we please at the moment ("not break faith") but to wait ("guard yourself in your spirit") until He reveals the one that He has created for us. If we do that, it will not end in divorce and it will not be a battleground.
"You have wearied the Lord with your words. 'How have we wearied him?' you ask. By saying, 'All who do evil are good in the eyes of the Lord, and he is pleased with them' or 'Where is the God of justice?'" NIV translation
Malachi warns the people that their words have "wearied the Lord" and He is getting tired of their words going against His Word. They are saying that evil is good and good is evil. That is the same today and even more so as many who teach the Word of God have clearly abandoned the Word of God. Just as God has called Judah to repentance here, in Malachi chapter two, He has called us to repent and turn back to God through His Word.