Psalms 78:22. Because they believed not in God, and trusted not in his salvation:

Refusing to Believe the Bible

Do you live a life of belief?  There are those who will not get saved because they refuse to believe in the God of the Bible.  They believe in a god, just not the true God of the Bible.  The reason it is not the God of the Bible they believe in, is because they trust in their own salvation, not “His” salvation.  When God provides the way to heaven through Jesus Christ and then you try to work your way there, that is a slap in the face of God.  First of all, it will never work.  Secondly, you are saying you know better than God what it takes to get into His heaven.

Only Christ’s Righteousness Will Do

You can only be saved by taking the righteousness of Jesus Christ to yourself by faith.  When you come to God, repent of your sin and believe on Him, and Him alone, to take your sin and give you His righteousness, you are coming God’s way.  God gave you Christ’s righteousness because there is no way you are ever going to get it on your own.  You come to God by simple, child-like faith and believe on Him.

Living a Sanctified Life By Faith

There are also those who get saved by faith, but then fail to live a life of faith in sanctification.  You need to let the grace of God work in your life to overcome the power of sin in the old man.  The new man needs to seek after God and trust him for deliverance and grace just like you did for salvation.  The sanctified life is a life of faith.  It has to be through God’s power or it will not work.  Otherwise it is a life of unbelief.  Do you live a life of belief or not?