Our testimony is invalidated if what we say is not totally based on personal experience. Hearsay is invalid in a trial; only personal testimony based on personal knowledge from personal experience is acceptable to hold weight in favor or against the person on trial.
This is why it is so vital that for God's sake we come to know Him personally and have a personal transformative experience of His grace in our life. Knowing facts about God or trying to keep up good religious appearances or 'live a good life' does not qualify as effective testimony in favor of God that will help vindicate His case. Jesus spoke about these kinds of attempts in His analogy of the judgment in His story of those surprised that their religious activities did not admit them into the kingdom. Significantly, the reason He gave for their disqualification was a lack of a personal relationship with Himself.
As a result, religious knowledge is only truly useful as it contributes to the enhancement of a personal relationship with God, not for a means of passing some mythical test to gain entrance into heaven. The Bible is not given simply to fill our heads with correct facts but to introduce and connect us with the God who created and redeemed us.
God is the one on trial, not us. In God's trial we all are witnesses. The effect of our witness in His favor is totally dependent on our willingness to allow God to do what He says He can do in our lives and to obey His instructions. His claims are being challenged by the world as being ineffective and spurious because most Christians fail to give Him full access to the center of their lives, to transform them into the image of God and look like Jesus. Who is really willing to let Jesus make them an experiment of grace to prove that God's claims are truthful? Who is willing to lay aside their own agenda, religious or otherwise, and allow God full access to every part of their life so He can demonstrate openly the power of His love and grace in a world unbelieving of His ability to save?
The lives that convey the most powerful witness in favor of the truth about God are often those who are viewed as least in importance from many people's perspective. Jesus stated very clearly that anyone who wanted to be great in heaven's eyes would need to be the most humble, the most caring for others and the least interested in looking out for their own desires. This concept is taught over and over throughout the New Testament particularly, yet as Christians we still overlook this most of the time. I suspect it is because this part of being a Christian makes us so uncomfortable that we want to move on to more appealing parts of our beliefs and try to ignore the hard instructions of Jesus.
But instead of seeing this as a hardship because it requires self-denial and dying to our own desires and plans, we could have a completely different attitude if we lived in the perspective of being witnesses in God's trial and valued the honor of contributing to His vindication. If we could get our minds off our narrow views of reality, our self-centered ideas of what life is about and be more cognizant of the far bigger context in which we are living, it would allow us to have totally different feelings about our circumstances and many of the things Jesus talked about as necessary to living as a Christian.
I have found it very helpful to remind myself of this larger context in which I live when in difficult situations. It helps me to put things into better perspective, to realize that life does not revolve about me but is a public courtroom in which all the universe is watching intently to observe what I am testifying about what God is like. Not only does my witness for or against God affect the interest of others making up their minds about whether to trust Him or not, but my testimony has a strong impact on the direction of my own life and impacts my own perceptions and relationship with Him.