If you are trying to speak the truth to someone, try praying to their Guardian Angel.
Have you ever tried arguing with someone about the faith, but never make any progress? Does the other person appear to have an obstinate heart, closed off to the truth?
St. Francis de Sales explains in his book Introduction to the Devout Life that one tactic we could try is praying to that person’s Guardian Angel.
It is generally believed that each person has a Guardian Angel, whether they are Christian or not, and that angel can help influence a person who refuses to listen to the truth.
That pious man [St.] Peter Faber, the first companion of Saint Ignatius, and the first priest, first preacher and first theological teacher of the Company of the Jesuits, who was a native of our Diocese, once passing through this country on his way from Germany, (where he had been labouring for God’s Glory,) told how great comfort he had found as he went among places infested with heresy in communing with the guardian Angels thereof, whose help had often preserved him from danger, and softened hearts to receive the faith.
St. Francis de Sales encourages individuals to recognize the presence of angels in all the places they go, sensing their invisible presence and seeking their aid.
Seek to be familiar with the Angels; learn to realize that they are continually present, although invisible. Specially love and revere the Guardian Angel of the Diocese in which you live, those of the friends who surround you, and your own. Commune with them frequently, join in their songs of praise, and seek their protection and help in all you do, spiritual or temporal.
Angels have been sent to us for our benefit and when we pray to them in faith, not wavering in our belief of them, we will be surprised at their hidden activity.