Testimonials about personal experience have a lot of power. This includes things pertaining to God and His Word.
The qualifier, however, especially for professing Christians, is this: Our experiences should not validate but be validated by what God has already said in His Word, the Bible (cf. 2 Tim. 3:16; 2 Pet. 1:20-21).
Of course, there's no denying the power of personal experience, even in Scripture. For instance, when Jesus healed the blind man in John Chapter 9, the fact that the man was 1) born blind, 2) healed in adulthood, and 3) reduced to begging, makes his testimony about the experience especially powerful. Who besides God and himself knew better what a miracle his healing was? That's why, after the Pharisees, refusing to acknowledge the obvious, accused Jesus of being a mere sinner, the exasperated healed man finally said, “Whether He is a sinner or not, I don’t know. One thing I do know, that whereas I was blind, now I see.” (v. 24-27,30).
If we know nothing else, we at least know what we’ve experienced, and like the testimony of a blind man who can suddenly see, nobody can take that away from us.
But even in this account, there is that qualifier. Jesus specifically said in this case that the reason the man was born blind was so that God’s power and perfect will could be shown in him. That healed man himself concluded, “If this Man were not of God, He could do nothing.”
He even told the insolent Pharisees, “I have told you [my testimony] already...why would you hear it again? Will you also be His disciples?” (v. 30). The point is that his personal testimony about his healing experience with Jesus was in line with what had already been written about God in the Scriptures up to that point (v. 34).
Consider also 2 Peter Chapter 1. First Peter says, “For we have not followed cunningly devised fables...but were eyewitnesses of His majesty” (v. 16; Matthew 17:1-5/Luke 1:2). But then he adds this interesting point (v. 19): “We have a more sure word of prophecy, unto which you do well that you take heed.” Even more powerful than what Peter saw and heard and experienced firsthand with Jesus is the fact that what he experienced was validated by what had already been written in the Word of God.
The truths of God which He provides in the Bible are not true because we experience them. Rather, we experience them because they are true. Whereas experience for the carnally-minded says, “If it works for me, then it’s right for me,” experience for the spiritually discerning says, “If it’s true in God’s Word, then it’s right for me.”
Christians should seek to experience, not what feels good or right according to us, but only what is in fact good or right and therefore worthy to experience according to God. And what is good and right and worthy according to God can only be determined by what He has already taught us in His Word, the Bible.