The message of the Gospel that's been committed to our trust is a pearl of great price. Therefore, we must see to it that it produces the desired impact and transforms the lives of those we minister to, by preparing their hearts to receive the Word; otherwise, the Word you share with them could be of non-effect.
The Gospel we've been commissioned to preach and teach is the only hope and power for the salvation of mankind. Therefore, the right prayer is very important for that message to transform lives. You have to travail in prayer; a form of agony of soul. In Luke 22:44, Jesus prayed that way: "And being in an agony he prayed more earnestly: and his sweat was as it were great drops of blood falling down to the ground."
The English word translated "agony" is the Greek "agonia", which means struggle, as to fight; like you're contending with someone for something. It's a wrestle, a fight of faith, a contention for the souls of men. In this kind of prayer, you're literally trying to seize those lives from the stranglehold of Satan.
Take for example, the case of a Christian who has become carnal, and doesn't take spiritual activities seriously. You'd have to "agonize" and travail in prayer for him so he could become spiritual and passionate about the things of the Spirit. He may have been out of Church, but you've decided to go share the Word with him, to strengthen and inspire him. Howbeit, you must first prepare his heart through this kind of prevailing prayer. Otherwise, he may listen to everything you have to say, and remain the same. But you don't want it that way! You want a change.
Therefore, agonize for his soul, pleading with tears in your heart on his behalf to God, that He would grant him repentance unto the acknowledging of the truth. As you do this, the Spirit of God will move on his heart, and grace will be released on his behalf for a change.