Adam Clarke on 1 John 5:18

Whosoever is born of God sinneth not - This is spoken of adult Christians; they are cleansed from all unrighteousness, consequently from all sin, 1Jn 1:7-9.

Keepeth himself - That is, in the love of God, Jde 1:21, by building up himself on his most holy faith, and praying in the Holy Ghost; and that wicked one - the devil, toucheth him not - finds nothing of his own nature in him on which he can work, Christ dwelling in his heart by faith.