If asked why Jesus became fully human and came to earth, I think most Christians would answer, “To die for our sins.” That’s certainly true, but when you think about it, He must also have come to do some teaching.
At a minimum, people had to be told of His sacrifice and what they had to do to avail themselves of it. What’s more, I think His elaboration on what God wants from us had to have been an important part of His mission as well.
Think of it: If Jesus just came to earth and was crucified for our sins without anyone being told of it, would that have been a satisfactory outcome? Presumably God also wanted people to know what had happened and why, and that, to achieve the salvation that Jesus sacrificed Himself for, a person had to acknowledge Jesus for who He was. And Jesus’ ministry was spent primarily in teaching people what their beliefs and actions should be (although He of course also said who He was and also mentioned twice — Matthew 20:28 and 26:28 — His dying for our sins). Surely He did not do all this radical teaching only because He happened to be in the neighborhood and just didn’t know what else to say.