Acts 16: 31: "Believe on the Lord Jesus Christ and thou shalt be saved."
The Greek word for believe is pisteuo: "to adhere to, cleave to; to trust, to have faith in; to rely on."
Do you abide in Christ daily? Being in Christ isn't saying a salvation prayer with words (lip-service salvation) and then that's it. There is no such thing as instant salvation. I believe there is such a thing as instant justification, but we work out our salvation every day with fear and trembling. "Take up your cross and follow me": this is something that we must do every day till we come into the fullness of Christ.
Do you daily adhere to Christ, have faith in Christ, rely on Christ? We receive daily manna (revelation) from heaven by being identified with Christ (submitted to Christ). The Lord will give us the gold, silver and precious stones of revelation, if we would believe in Him every day.
Believing should be just like breathing: we stop breathing, we die physically; we stop believing, we die spiritually. Unbelief is sin.
"Enough! the Resurrection,
A heart’s-clarion! Away grief’s gasping, ' joyless days, dejection.
Across my foundering deck shone
A beacon, an eternal beam. ' Flesh fade, and mortal trash
Fall to the residuary worm; ' world’s wildfire, leave but ash:
In a flash, at a trumpet crash,
I am all at once what Christ is, ' since he was what I am, and
This Jack, joke, poor potsherd, ' patch, matchwood, immortal diamond,
Is immortal diamond."
--Gerard Manley Hopkins
Are you Christ-identified?
From The Amplified Bible: "And they answered, Believe in and on the Lord Jesus Christ--that is, give yourself up to Him, take yourself out of your own keeping and entrust yourself into His keeping, and you will be saved; [and this applies both to] you and your household as well." (Acts 16: 31)