Everyone born out from God does not habitually sin because His seed abides in him and he is not inherently able to sin because he is born out from God (1 John 3:9).
The apostle John is not stating that a Christian will not sin; that concept would contradict the beginning of his letter, where he instructs us on what to do when we sin. He is stating that, because God’s seed is in us, we are now incapable of living a habitual life of sin. The moment we function from our spirit and relate to God, we cease from sinning. Our birth comes from an incorruptible seed (1 Peter 1:23). It is a spiritual birth; therefore, when we are emanating the things of the Spirit of God, we are able to understand spiritual concepts and apply them to our lives, resulting in a life apart from sin.