You will often hear heretics demanding “Show me where Jesus said...". While Jesus said a lot of things, there are many unpopular doctrines found throughout scripture that did not directly proceed from the human mouth of Jesus (at least as far as we have on record). If Jesus did not directly touch on a specific doctrine, heretics often take that as permission to reject it.
The greatest problem with this reasoning is that Jesus actually gives authority to all the scriptures, meaning even if He isn’t recorded as having said it with His human mouth, you cannot believe the “red letters” without also believing the black letters. Jesus said, for example, said to His disciples “He who receives you receives me...” (Matthew 10:40a, emphasis mine). Therefore, you cannot believe those red letters without accepting the black ones written by the apostles to whom they were spoken. So, using the Trinity as an example, even though Jesus never explicitly said "there is one God who exists in three separate persons", John 1 is a very strong argument for the Trinity.
Paul was also sent by Jesus, and he said that all scripture is “God breathed” (2 Timothy 3:16). Since Jesus is God, all letters in the Bible should be red. It’s therefore time to stop with the silly logic that if Jesus didn’t explicitly say it, therefore it isn’t true. If you are a Christian, the entire Bible is fair game. Take it in its correct context, or don't take it at all. But if you don't take it at all, cease with your claims to be a Christian, because you cannot love Jesus without obeying Him (John 14:21-24).