And telling non-believers/scoffers that their father is Satan is going to produce fruit?
Some of those most violently opposed to God have become the strongest professors of the faith. I shudder to think what you would've said to Paul/Saul before his conversion.
But the fruit of the Spirit is love, joy, peace, longsuffering, gentleness, goodness, faith, meekness, temperance: against such there is no law.
Galations 5:22-23
Which one of those "fruits" fits with calling someone the son of Satan?