Someone might answer: "We could still sin against Him in ignorance." But the perfect love with which we are called to love God is a perfect love of our minds as well as our hearts. If we perfectly loved God with all of our minds, from whence could this ignorance flow? One who loves God perfectly with the mind is perfectly diligent in studying and mastering the Word of God. The perfectly loving mind perceives correctly the light into our paths. A perfectly loving mind doesn't make errors in understanding Scripture.
But could we not still make mistakes because our minds are less than perfect? I ask why our minds are less than perfect. It is not because we lack brains or the faculty of thinking. Our thinking is clouded because our hearts are clouded. Take away the cloud from our hearts and our minds are illumined by the clear light of God.
A perfect love would yield perfect obedience. The only perfected love this world has ever seen was the love of Christ, who exhibited perfect obedience. Jesus loved the Father perfectly. He sinned not at all, either willfully or in ignorance.
Excerpt from R.C. Sproul's, Pleasing God.