For by you I can run against a troop, and by my God I can leap over a wall. (Psalm 18:29, ESV)
The non-Christian's doctrine of positive thinking believes that a strong optimism even in the face of contradictory circumstances result in greater happiness and attainment in life. Confidence in one's self releases human potential and dissolves mental blocks to success, and empowers one to seize his dreams and achieve desirable outcomes.
However, this optimism is unfounded and results from delusion. The non-Christian man is depraved through and through. He is dead on the inside. He is a walking corpse, and all his faculties are defective. His optimism makes himself into an idol, and blinds him even more to the God who is the master of his fate and the Christ who is only the savior of the soul.
On the other hand, the Christian has more reason for positive thinking and an extreme optimism than any non-Christian. The Christian has been regenerated, and the Spirit of God infuses life and power into him, healing and renewing him from the inside out. So it is ironic that much of Christian teaching, in opposition to Jesus Christ, advances a deadly pessimism that drains the life out of God's people, and rots their bones and their very souls.
Yet a Christian's confidence is not in himself, but in God who is without limit in his ability and wisdom. As Paul wrote, "I can do all things through him who strengthens me" (Philippians 4:13, ESV). This does not mean that a man of faith never faces hardship, for in this statement Paul referred to his ability from Christ to remain content in any situation, even when he had to endure hunger and poverty.
Although this suffering faith has been disproportionately emphasized, God's people in general remain feeble and whiny. This is the case because most preachers and theologians cannot teach anything right, so suffering faith is taught in a way that produces people who suffer without much faith at all. And perhaps the people remain feeble and whiny precisely because suffering faith has been disproportionately emphasized, and an entire realm of faith has been unexplored.
A Christian's faith is not only a suffering faith, but it is also an overcoming faith. It does not only put up with things, but it also changes them. It is a faith that acts. It is a faith that wins. Just as Paul wrote that by Christ he could suffer hunger and poverty, David said that by God he could go against an army and leap over a wall.
Human tradition lulls people into a loser piety, so that while wallowing in self-pity and defeat they could congratulate themselves for being so spiritual. Then they would not know to interrogate their church leaders and the theologians as to why believers do not have more power and victory in their lives.
But Jesus introduces us to all the possibilities of faith. He said, "For truly, I say to you, if you have faith like a grain of mustard seed, you will say to this mountain, 'Move from here to there,' and it will move, and nothing will be impossible for you" (Matthew 17:20, ESV). If you have faith, nothing will be impossible for you. Nothing will be impossible. You can even command a mountain to move, and it will happen.
This is far more than a matter of human potential. It is positive thinking on a whole different level, because it reaches into the realm of miracles, into the realm of God and the powers of the coming age. Jesus talked about this over and over again. He wants us to know that this power does not belong to the apostleship or to a certain century, but it belongs to faith. And it belongs to you, if you believe.