The fact that our salvation involves being trained by grace to obey God implies that we do not become perfectly obedience on the day that we accept Christ. In Philippians 1:6, he who began a good work in us will be faithful to complete it on the day of Christ Jesus, and if we became perfectly obedient when we accepted Christ, then there would would be nothing left to complete on that day, so it is an ongoing process that will not be completed until then. So if we sin, then we will repent. Again, if we needed to have perfect obedience for some strange reason, then there would be no point in reptance because it would already be too late to have that, so the fact that repentance has value means that obedience that is less than perfect has value.