Philippians 1:5-6 "5 because of your partnership in the gospel from the first day until now, 6 being confident of this, that he who began a good work in you will carry it on to completion until the day of Christ Jesus."
No man can live up to God's standard of sinlessness in this life. Only Christ in us is sinless and His blood covers us. Just like the account of the Jews protected by the blood smeared on the doorposts when the Spirit of God saw the blood and passed over the Jews for judgement, so are we covered in Christ's blood.
None of my attempts to be good will gain me heaven, before or after salvation. It's all about Christ. When I trusted what He did for me, then He imputed to me His sacrifice on the cross, because you see...I could not die for my sins, it had to be a Sinless Perfect One Who did that, I do not qualify. Just as I cannot die for my sin, how silly to think that I could try real hard to be good to keep salvation that required the death of the perfect sinless God?
I am thankful that Christ took it all upon Himself, that I might be seen as righteous. His righteousness is accounted to me.
Even the smallest sin could have kept us out of heaven, but because of Christ NO sin will keep us out if we have trusted Him. HOWEVER, when we become born again He changes our desires, we no longer want to sin, but we sometimes fail. That's why Christ gave us 1 John 1:9, written to believers.
"9 If we confess our sins, He is faithful and righteous to forgive us our sins and to cleanse us from all unrighteousness."
AND, 1 John 2:1-2 "1 My little children, I am writing these things to you so that you will not sin. But if anyone does sin, we have an advocate before the Father — Jesus Christ, the Righteous One."
Only those who belong to Christ have an advocate. They have an advocate because they sin.
We do not want to sin, we hate it, but we fail, that failure does not lose us salvation, it may make us miserable, the consequences may overwhelm us so that we will confess that sin and return to fellowship with Christ.
We cannot lose our salvation if we have been born again into a new creation, but we can lose fellowship with Christ until we confess and return to obedience. When we refuse to listen to the Holy Spirit that lives in us, then He will stop speaking to us until we come back into fellowship with Him through humble submission.
1 Corinthians 1:8-10
"…8 He will sustain you to the end, so that you will be blameless on the day of our Lord Jesus Christ.
9 God, who has called you into fellowship with His Son Jesus Christ our Lord, is faithful.
10 I appeal to you, brothers, in the name of our Lord Jesus Christ, that all of you agree together, so that there may be no divisions among you and that you may be united in mind and conviction.…"
Ephesians 4:30
"And do not grieve the Holy Spirit of God, in whom you were sealed for the day of redemption."
1 Thessalonians 5:18-19 "…18 Give thanks in every circumstance, for this is God’s will for you in Christ Jesus. 19 Do not extinguish (silence) the Spirit. 20 Do not treat prophecies with contempt,…"
Keep in mind that disobedience to Christ can leave us with very sad and devastating consequences, often life long. We cannot expect to test God and remain unscathed by the affects of sin.