'Certainty' in the Bible

so that you may know the exact truth about the things you have been taught [that is, the history and doctrine of the faith].

knowing [with all certainty] that it is from the Lord [not from men] that you will receive the inheritance which is your [greatest] reward. It is the Lord Christ whom you [actually] serve.

for our good news [regarding salvation] came to you not only in word, but also in [its inherent] power and in the Holy Spirit and with great conviction [on our part]. You know what kind of men we proved to be among you for your benefit.

This hope [this confident assurance] we have as an anchor of the soul [it cannot slip and it cannot break down under whatever pressure bears upon it]—a safe and steadfast hope that enters within the veil [of the heavenly temple, that most Holy Place in which the very presence of God dwells],

You too, be patient; strengthen your hearts [keep them energized and firmly committed to God], because the coming of the Lord is near.