As a Christian, a disciple, a follower of Christ, if we have confessed Him as Lord and Savior then we need to act like it. Our behaviors should be determined by our belief. We don’t determine our beliefs based on our behaviors or by our experience or even our feelings. We look at what Jesus said, what He told us to do and we endeavor with the strength that He gives to do it. That is not legalistic. That is obedience. Legalism is when our salvation is determined by our works. True Christianity is expressed by a person who is doing the works of Christ, not to earn His love, but because we know we have it. But if we are not doing it, if we are deliberately walking in disobedience and sin and we will not receive the correction of the Holy Spirit or we will not receive the correction of brothers and sisters in Christ, then there is a very real possibility that we are not truly saved.
Yes, all believers struggle with sin and some more than others, but we must not rationalize and excuse it, we can’t just shrug it off as “no big deal”, we must be at war with sin. As John Owen said, “be killing sin or it will be killing you.”