For this is the love of God, i.e. this is the most lively, certain expression and effect of our love to God, our keeping his commandments, which are so little grievous, that true love can make no difficulty of doing so, Matthew 11:30 Psalms 19:11.
Related Commentaries of 1 John 5:3
1 John 5:3
3 For this is the love of God, that we keep his commandments: and his commandments are not grievous.