I't is simple ,sinful mankind had to have a perfect man to redeem us from certain death that is sin. So JEHOVAH GOD sent his son to earth to #1 Teach the good news about the bible and how JEHOVAH GOD has a plan for the earth that he had created and will never be destroyed, and also to die for us so that we have a chance to gain everlasting life here on this planet.

The idea of Father, Son, and Holy Ghost is difficult to explain, probably because our understanding is imperfect.
I can see how that would make it harder.

His message was, "Have faith in Me, repent, and you will have eternal life." I would say it did not reach many people in His time or in ours.