"If I testify about myself, my testimony is not valid. There is another who testifies in my favor, and I know that his testimony about my is valid." John 5:31-32
Jesus is talking about how even though he is the Son of God, that his testimony was validated only through the rest of the Bible and how it pointed to him. that, although some people may have doubts about his claims, or his "testimony", that they could search through Scriptures and for that matter the wisdom of the created world and find that what Jesus was saying was and is true. He is God become Man so that He could live a perfect life and save the world from the sin that is destroying it.
On a day like today, feeling crummy and very much an invalid, I need to know that someone is giving testimony for me. That even though my life doesn't show that the hope of Christ is in me...I hope that Christ is even now giving testimony to the Father that I am indeed one of his children. That when I am too apathetic, too self-consumed, too you name it - when my testimony becomes invalid...He still speaks up for me and claims me.
As Job once said, I know that he lives