"Does not sin" is in the durative present tense in the Greek which means it is describing a walk, a lifestyle. A literal translation would be, "Whoever abides in Him does not sin on and on." Our Father doesn't expect us to never sin, but He does expect us to sin less and less.
1 John 3:4-9; NKJV
4 Whoever commits sin also commits lawlessness, and sin is lawlessness.
5 And you know that He was manifested to take away our sins, and in Him there is no sin.
6 Whoever abides in Him does not sin. Whoever sins has neither seen Him nor known Him.
7 Little children, let no one deceive you. He who practices righteousness is righteous, just as He is righteous.
8 He who sins is of the devil, for the devil has sinned from the beginning. For this purpose the Son of God was manifested, that He might destroy the works of the devil.
9 Whoever has been born of God does not sin, for His seed remains in him; and he cannot sin, because he has been born of God.
