If I bear witness of myself - If I have no other evidence than my own testimony about myself.
My witness - My testimony; my evidence. The proof would not be decisive.
Is not true - The word “true,” here, means worthy of belief, or established by suitable evidence. See Matthew 22:16; “We Know that thou art true” - that is, worthy of confidence, or that thou hast been truly sent from God, Luke 20:21; John 8:13, John 8:17. The law did not admit a man to testify in his own case, but required two witnesses, Deuteronomy 17:6. Though what Jesus said was true John 8:13, John 8:17, yet he admitted it was not sufficient testimony alone to claim their belief. They had a right to expect that his statement that he came from God would be confirmed by other evidence. This evidence he gave in the miracles which he performed as proof that God had sent him.