Question: Why didn’t Jesus perform more miracles while he was still alive to further prove that he was truly the Son of God? Also, why didn’t he leave personally written documents or manuscripts stating his teachings?
— Kevin Fellman, via email
Answer: The premise of the first question is debatable. Jesus worked many miracles. So many in fact that John would later remark: “There are also many other things that Jesus did, but if these were to be described individually, I do not think the whole world would contain the books that would be written” (Jn 21:25). That said, Jesus did in some ways limit his miracles when he sensed that there was little faith in the request or when he sensed his ministry was being treated as a sideshow by some. Of Nazareth, it is said, “So he was not able to perform any mighty deed there, apart from curing a few sick people by laying his hands on them. He was amazed at their lack of faith” (Mk 6:5-6). In another place, “While still more people gathered in the crowd, he said to them, ‘This generation is an evil generation; it seeks a sign, but no sign will be given it, except the sign of Jonah'” (Lk 11:29). The Pharisees would often demand signs, not in faith, but in effect, they were taunting Jesus: “Force us to believe in you.” At some point, no amount or caliber of miracles would convince some of them. After three years of working miracles, Jesus still had many who refused to believe. He laid out a case for them of four proofs that he was Messiah and Lord: The testimony of the Father in their hearts, the miracles he worked, the huge number of Scriptures he fulfilled and the testimony of John the Baptist (Jn 5:31-45). So, he gave them more than miracles as proof. Yet still many of the leadership would not believe in him.
As to your second question, you are right that he never wrote a letter or book. He left that to the apostles who were eyewitnesses and who received the Holy Spirit to remember everything he did and taught (Jn 14:26). More precisely, either they dictated the Lord’s teachings to scribes or members of the early Church wrote down what they preached. This is because writing was a rare skill and one not likely possessed by these largely working-class men. Whatever the exact method, we know that we have the text of Scripture just as it needs to be because of the gift of the Holy Spirit, mentioned by Jesus.