Matthew 19:23 "Truly I tell you, it is hard for someone who is rich to enter the kingdom of heaven."
It is hard for a rich man to enter heaven simply because it is hard for him to depend God. God love His children to depend Him for each and everything. God love us to depend Him for all our needs which includes all life sustaining needs such as food, water, healing, etc. and all material needs such as dress, footwear, shelter, electronics, vehicle, etc. and mental needs such as happiness, peace, hope, faith and spiritual needs such as salvation, holiness, Holy Spirit, protection, etc. and other needs such as education, job, wisdom, knowledge, etc.
Depending God for all things can develop a very strong attachment with God. The attachment develops in a new born baby to his mother by depending her for almost everything is a very good example. Depending God for all our needs is quite easy and practically possible, when we don't have other options. When we have other options, depending God is not quite easy. Being rich or having plenty of money is an excellent option not to depend God, especially for our material needs. If we don't have any or enough money for our daily bread, we will pray literally from our heart to God to 'Give us this day our daily bread.' When we are rich, our daily bread will be available sufficiently and we don't depend God for the same. Most of all of us are becoming rich day by day. If we notice, we can realize that we do not depend God in our richness as we were in our poverty. Depending God for our health issues in poverty and depending medicines and physicians in our richness is a very common thing. Getting our material needs satisfied instantly by purchasing it with money rather than depending God is another example.
Progressively depending richness bring a person into a situation not to depend God for everything he is able to attain with his money. This will affect a person's relationship with God. It will reduce his trust in God and increase his trust in richness. After all it will bring the person into a situation where he will not be able to trust God for his needs and not in his riches. Let me ask each one of you the same question Jesus Christ asked to the rich man more clearly.
Can you sell Everything you posses today, Trust God and Face tomorrow?
If you cannot, look back to the time you don't posses much riches. Then you will realize that there was a time you were able to do so because you trusted God so much and gradually your trust now changed from God to money. This is the same thing happened with the young rich man. He is not able to trust that God will be able to nurture him if he sell his riches.
Hope you understand now why is it hard for rich man to enter heaven.