Jesus must have read the heart of the man who questions Him about getting to Heaven. Jesus doesn't call him out about obedience to the law or the goodness of his heart. We must assume, from what Jesus does not say, that the man was truthful - he obeyed Jewish law. The man has done nothing wrong, yet he has not gone far enough. Jesus calls him to go beyond earthly laws (Jewish dietary regulations, etc.) and to the cross, to sacrifice and follow Him. What can this man sacrifice? He is rich, so his sacrifice is money.
Now, money is not evil in itself. Money, though, must be a means rather than an end. Money is not necessary itself but can be used for necessary things (e.g. food). Why, then, is it hard for a rich man to enter Heaven? Because excessive money, like excess of nearly anything, is addictive. As Venerable Bede wrote, "there is a great difference between having riches, and loving them". When you have a lot of money, your thoughts can easily turn to protecting, rather than using, your money. Rather than use your money in expressing your love of others, your love turns to money itself as its object.
Each of us is this man. We each have something of this earth to which we are too attached. If you're over-attached to money (whether you actually have it or not), then you must overcome that attachment that draws your focus from Christ. Alcohol is not itself evil. (Jesus did not pass Welch's around the table at the Last Supper.) You must, though, be sober to walk steadily after Christ. Sex is not itself evil; we are commanded from the very beginning to be fruitful. Sex is a mean to the end of producing life. If you are too focused on sex, you cannot focus on the Author of life.
I beg of you, my Lord to remove anything which separates me from you, and you from me.
Remove anything that makes me unworthy of your sight, your control, your reprehension; of your speech and conversation, of your benevolence and love.
Cast from me every evil that stands in the way of my seeing you, hearing, tasting, savoring, and touching you; fearing and being mindful of you; knowing, trusting, loving, and possessing you; being conscious of your presence and, as far as may be, enjoying you.
This is what I ask for myself and earnestly desire from you. (Blessed Peter Faber)
Blessed Peter Faber Prayer for Detachment, cited by Bernaccio, P., Online at http://aseedinbriar.blogspot.com/2009/09/blessed-peter-faber-prayer-for.html
St. Thomas Aquinas, Catena Aurea: Gospel of Matthew. Online at http://www.catecheticsonline.com/CatenaAurea-Mark10.php