By the same token, a Christian can go to a population and in charity, motivated by love for God first of all, help provide food, shelter, clothing, medical care, etc, and hardly speak at all of what he believes, and gain a far greater number of converts than the zealous preacher who has little charity, because the people in the first case will be aroused by the charity of the one, and will inquire about the beliefs that are made attractive because of the charity.
Charity is like the seedbed for fruitful conversions. Like Saint Paul said, without charity, our preaching is like a clanging cymbal. And when the preaching and teaching includes a lot of judgment and harshness, no one is going to be attracted to that.
Also, God's grace accompanies the practice of charity. The gentle, humble, prayerful soul that goes about doing good, helping the poor, the sick, the lonely, will be supported by God's grace. I don't think we can say the same, consistently, about the teacher/preacher who simply teaches, preaches, condemns, even if in perfect truth, if his words are not accompanied by practical charity.
It is the same in parenting or in leading. People usually have a far more positive response and a far more positive memory of a father who tells the truth and teaches and corrects by an example of humble conviction lived out in gentleness and charity. People never grow up and complain: "My father was so damned loving, I wish he had been less forgiving and gentle." No, they complain about a father who was harsh, whose beliefs were overshadowed by harshness and justice and an inability to love. For the child looking back, what he remembered was a hypocrite who put correcting error above love and forgiveness.
As tough as Jesus could be with sinners, especially hypocrites, he readily forgave any who repented, and his miracles benefited all who were willing to believe.