And to whom did he swear that they would not
enter his rest, but to those who were disobedient?
So we see that they were unable to enter because
of unbelief. Hebrews 3: 18 – 19

According to the scripture from Hebrews above, biblical unbelief is equivalent to disobedience.
† The way that it is used in the Bible, belief involves or requires some action in obedience to God. It is not just a description of how you think or feel.

The Bible instructs us that we should believe:
† In God and that He rewards those who seek Him
† That Jesus is the Christ and the Son of God
† That Jesus died on the cross to pay for our sins, that what He did on the cross was sufficient to pay for our sins and that only He can pay for them
† That He was raised from the dead and that God will raise us from the dead also

…for whoever would draw near to God must believe that he exists and that he rewards those who seek him. Hebrews 11: 6b

but these are written so that you may believe that Jesus is the Christ, the Son of God, and that by believing you may have life in his name. John 20: 31

…believe in your heart that God raised him from the dead… Romans 10: 9b

If you really, truly believe a building you are in is on fire, it will influence your actions. Likewise, if you truly believe the points above, it will directly influence how you act also.