God doesn't like jealousy, let's just get that out of the way. So if you're feeling jealous of what other people have, stop yourself immediately. This is the work of the devil and the devil alone. If you want to know why jealousy is wrong on so many levels, let's look at what the Bible says about it here.
Jealousy is a result of envy
Let us not become conceited, provoking and envying each other. – Galatians 5:26
One of the seven deadly sins is envy. So if jealousy stems from envy, there is no doubt that jealousy is an evil thing. How do you know if you're feeling jealous? It is when you feel envious of other people because they have what you don't. This shows a lack of control of yourself and more importantly, that you are being controlled by your earthly desires. Jealousy is a sick cycle because the reality is that there will always be other people who will have what you don't.
True love is not jealous
Love is patient, love is kind. It does not envy, it does not boast, it is not proud. It is not rude, it is not self-seeking, it is not easily angered, it keeps no record of wrongs. – 1 Corinthians 13:4-5
Another thing that makes jealousy so evil is because it is the opposite of what true love is. 1 Corinthians 13:4-5 says that love does not envy. There are so many relationships and marriages that were destroyed because of jealousy. Even families have been divided because of jealousy. Jealousy brings about hate in relationships. It also causes distrust and selfishness because you're only focused on your own desires when your focus must be on God. If hate takes over your heart, your heart will harden and this will push away God in your life. Now, do you see the cycle?
Jealousy shows lack of contentment
Keep your lives free from the love of money and be content with what you have, because God has said, 'Never will I leave you; never will I forsake you." - Hebrews 13:5
God has given us so much, more than what we deserve. Ask yourself, isn't that enough? For some, it is. But for others, they are still not satisfied with what God has given them. In Hebrews 13:5, God commanded us to not love money and be contented. Hence, being covetous goes against what God wants us to do.
Jealousy pushes God away
Do not conform any longer to the pattern of this world, but be transformed by the renewing of your mind. Then you will be able to test and approve what God's will is—his good, pleasing and perfect will – Romans 12:2
There is only one way to fight jealousy that's brewing in your heart, and that is to always remember to be more like God. The cold hard truth is it is easier to give in to the wickedness of the world than to stand our ground and commit to our beliefs. It is definitely easier to just feel jealous than control your emotions, doesn't it? However, God wants you to fight worldliness everyday. And if you let him into your heart completely, then you will have a partner in fighting this war for life. Let God stay in your heart, so no evil can occupy it.