Only God knows what lies at the depths of the hearts of men and women (Sir 42:18). He knows what will reach a person's heart and what won't. We Christians, who are charged with making disciples, are "fishers of men" (Mt 4:19). We are like fishermen casting a line. Fishermen generally see only the surface of the water, not the fish under the water. Likewise, we see the outside of a person to whom we witness, but not the inside, while the Lord sees the inside as well (1 Sm 16:7). We Christians need "inside information" if we are to reach a human heart.
When Jesus called us to be fishers of men, He gave us the Holy Spirit to teach us to fish. The Spirit gives us that inside information, teaching us at any given "moment all that should be said" (Lk 12:12). If we use our own words, they might be eloquent, but they will ultimately be ineffective in catching men. However, the Spirit's words spoken through us will reach hearts.
Jesus, working through the Spirit, "will give [us] words and a wisdom" that those to whom we witness cannot oppose or contradict (Lk 21:15). Let us constantly, moment by moment, seek the Holy Spirit. He is the Master Communicator, and is able to teach us what to say. "Since we live by the Spirit, let us follow the Spirit's lead" (Gal 5:25). Come, Holy Spirit!