Hymns should preach. Hymns should proclaim. Hymns should confess. Good hymns do all of that in a masterful way; they preach a sermon that is eloquent, that is simply, that is conveyed through the blessed medium of music. Good hymns don't simply play with the emotions; good hymns have something to say.
When good hymns preach, they are not simply preaching to someone. In fact, our preaching, whether from the pulpit or in the song of the Church, should never be simply to the people in the pew or even to the world. Good preaching is also against someone or something.
The hymns of the Church should speak a word against our own flesh, putting it to death. The hymns of the Church should speak a word against death, telling our ancient enemy that it has no hold on God's saints. The hymns of the Church should speak a word against Satan, telling Him to cease His accusations and go back to hell where He belongs.
Not every hymn has to do this explicitly to be a good hymn, but especially the great hymns of Easter and Baptism do this marvelously. The hymns of Easter preach the victory of Christ against death itself. Many of them have this 'in your face' attitude, telling death that its reign is done with the death and resurrection of the Son of God in our place. The hymns of Baptism are especially suited for this, because in Baptism, God takes hold of a person and seizes him or her from the dominion of sin, Satan, and death. "God's Own Child, I Gladly say it" embodies this perfectly: "Satan, hear this proclamation: I am baptized into Christ! Drop your ugly accusation, I am not so soon enticed. Now that to the font I've traveled, all your might has come unraveled, and against your tyranny, God, my Lord, unites with me!" On Easter, on the occasion of a baptism, and every Lord's Day, we sing to our enemies, but we also sing against our enemies, only because Christ Himself has won the victory for us.