Perseverance is an important doctrine to understand, because unless we persevere in faith we will not be saved. If you stop believing your belief was in vain. The Christian life is a war that is a life long fight of faith. You will fight sin until you die or you will loose (see 2 Timothy 4:7), but all who are justified will win this fight (not spared this fight) and persevere in faith (thought there may be seasons of backsliding) because "Perseverance" is the promise of the New Covenant.
In our study of scripture, we need to be honest about what Biblical threats that require perseverance (and sound like believers can loose their salvation) imply about God's people, and not ignore them. We cannot solve the issue of security and assurance by just avoiding those texts that sound threatening to professing believers.
In the video below, John Piper looks first at the threatening texts (like 1 Corinthians 15:1, Colossians 1:21-23) to sober us up by the requirement of perseverance and then texts that show the gift and assurance of personal perseverance.