"I am the Lord; that is my name! I will not yield my glory to another or my praise to idols." (Isaiah 42:8)
Imagine that you just proposed to your future wife and she said that she would marry you as long as you let her bring her ex-boyfriends to shack up with you all in the house. Or that your future husband wants you to let his ex-girlfriends move in right after he carries you over the threshold or he won't go through with the wedding. Would you put up with that? No! That would be unreasonable and insulting. Yet, that is what you are asking God to do when you expect Him to let you into heaven when you practice a different religion or have idols in your life.
When you get married, you need to cast aside all members of the opposite sex besides your spouse and make your wife (or husband, if you are a woman) the only love of your life. It is only under those circumstances that you will truly experience the amazing emotional and sexual fulfillment that God intended for you to have. Likewise, when you come to Christ, you must remove anything else in your life that is competing for your love and worship. It is only under those circumstances that you will truly experience the amazing love and spiritual fulfillment that God intended for you to have. This includes things which are normally good, such as family, work, and money. This doesn't mean that you should give up all your worldly possessions and live a life of solitude in a cave in Utah. It simply means that if you have to choose between God and those things, you must choose God. In order to choose God, you must choose His Son, because Christ is the only way to get to God.
"Jesus answered, “I am the way and the truth and the life. No one comes to the Father except through me." (John 14:6)
Marriage, when "exclusive" between a man and a woman, and pursued selflessly, is the best possible human relationship. Following Christ is like that, but to the infinite power. When it is an exclusive, selfless relationship between you and Jesus, it is the best possible relationship that you will ever have. Period.
