It really is as simple as that. For believers, anyway.
Anyone who claims to know God necessarily cares about pleasing Him. Sin is the opposite of pleasing Him. If you do not want to please Him, do not say you know Him. You don't. Best case: you are deceiving yourself. You think it is, but the truth is not in you. (1 John 1:8)
Here is what every Christian does concerning sin. They stop it. The keep from it. They do not do it. Will they struggle? Of course. Fall? Yes. But they never stop working to stop their sin. They love God too much.
John, the good shepherd of his flock, writes the letter of 1 John, in part, because his precious children of the faith are sinning. He tells them to do what Christians do: stop.
Christians have a tendency to do one of two things when told not to sin. They offer a hearty "amen", adding that it is by not sinning that Jesus' forgiveness is triggered or maintained, OR they offer resistance, claiming that they are free to sin, because Jesus has paid the price for their forgiveness.
The first people make up the "you better get it right" church. The second group of people make up the "don't worry about obedience" church. Neither make up Christ's church. Christ's church is made up of people who allow the Holy Spirit to make sense of this paradox.
See, believers know that, indeed, "If anybody does sin, we have one who speaks to the Father in our defense - Jesus Christ... the atoning sacrifice for our sins." (2:1-2) But they also know that, "If anyone obeys his word, God's love is truly made complete in Him." (2:5)
This is not complicated for believers, because they know how to go deep, into spiritual and Kingdom truths, where actual, experiential relationship with God makes it all make sense. Others stay in their heads, picking the half of the Bible's verses to quote - the ones that support their half of the gospel message.
I think this is why Paul says that those with the Spirit get it, those without do not. (1 Corinthians 2:14)
Those without the Spirit are either/or people. They claim to know God, but they either defend their right to sin OR are determined to promote a gospel that says you must stop sinning or risk losing your salvation.
They really do believe they know God. John gives his precious flock this benefit of the doubt when he says they are self-deceived. But today's passage is John's way of saying what Jesus said in John 14:15 - "If you love me, you will obey my command."
What can I say? If you get it, you get it. And according to John, this is important to get.