One interpretation is that in chapter 3 John means that Christians don't persist in sin. They don't continue to commit the same sin with no thought of repentance, confession, or change. The author of Hebrews seems to share this opinion in 10:26 when he writes, "If we deliberately keep on sinning after we have received knowledge of the truth, no sacrifice for sins is left."
When we are baptized, we receive grace to help keep us from sin. And God continues to give us this grace, this help along the path. If we use the grace we are given, and continue to ask for more help from the Holy Spirit, the habitual sins of our past should fall by the wayside. We continue to become more like Jesus every day.
For Reflection: Do I have a persistent sin in my life? Have I repented and confessed it? God's grace is sufficient for any situation.
Let us pray. Jesus, your grace is sufficient because you died for me. Your grace is sufficient because your mercies are new every morning. Your grace is sufficient because you are faithful and true.