"And they also, if they do not continue in their unbelief, will be grafted in, for God is able to graft them in again."
"Today if you hear His voice, do not harden your hearts." Hebrews 4:7 (quoted from Psalm 3:19b-20)
We have to get to where we believe God and His words no matter what. We have to believe -- especially when it is dark all around us; especially when we are facing the Unknown; especially when things are confusing, devastating, hopless -- ESPECIALLY THEN!
Read those verses again -- unbelief kept God's kids from entering His rest, His peace.
"For indeed we have had good news preached to us, just as they also; but the word they heard did not profit them, because it was not united by faith in those who heard." Hebrews 4:2
We can make God's word useless in our lives. We can take away its power when we refuse to believe, when we get too scared to have faith when what we see contradicts what God says.
Don't do this! Living a life of believing-no-matter-what can be very scary but so exciting and will plug you into reality, the true reality more than anything else can!
Unbelief is a sin. It is a really bad sin.
Because it keeps us from God. And because without it we have no hope of pleasing Him.
"without faith it is impossible to please Him" Hebrews 11:6a
Unbelief often masquerades has good behavior, religious rule-keeping, rationalism, and "being practical."
And if you choose to live with the believe-no-matter-what mentality be prepared to be misunderstood and judged because it takes a lot of courage to live this way. And many choose not too.