'Assurance' in the Bible

For all that is in the world—the lust and sensual craving of the flesh and the lust and longing of the eyes and the boastful pride of life [pretentious confidence in one’s resources or in the stability of earthly things]—these do not come from the Father, but are from the world.

Now, little children (believers, dear ones), remain in Him [with unwavering faith], so that when He appears [at His return], we may have [perfect] confidence and not be ashamed and shrink away from Him at His coming.

Beloved, if our heart does not convict us [of guilt], we have confidence [complete assurance and boldness] before God;

In this [union and fellowship with Him], love is completed and perfected with us, so that we may have confidence in the day of judgment [with assurance and boldness to face Him]; because as He is, so are we in this world.

This is the [remarkable degree of] confidence which we [as believers are entitled to] have before Him: that if we ask anything according to His will, [that is, consistent with His plan and purpose] He hears us.