The word catechesis, in Greek—katékhéo—comes from the two words kata-ekheo. But kata-ekheo means to “echo down” or, you might say, to “echo precisely.” St. Paul and St. Luke used this word (see, e.g., Lk 1:4 and 1 Cor 14:19) to explain what we are doing when we teach the Christian faith. They are telling us that a catechist and his teaching are supposed to be an echo, a precise echo, of what has been given for instruction.
But if I am just an echo, then that means the original voice is someone else’s. The Kerygma, the good news of the Lord, is supposed to resound as we hand down our faith.