"Thou wilt keep him in perfect peace, whose mind is stayed on thee: because he trusteth in thee" ~ Isaiah 26:3
How to think peaceful thoughts: "... whose mind is stayed on thee." This much is widely used. It is a mental discipline. Focus your mind on your own concept of God, the new thought books say, then you will find peace.
But, true peace cannot be found. It is a gift of God. "He is our peace," says Paul, and the "He" is Jesus Christ who has "made peace by the blood of his cross." There is psychological value in the very act of keeping one's mind fixed on something outside of oneself. Something "higher." But when your heart is smashed you can't focus your mind most of the time. When your body is trembling with pain, you can't practice concentration. This is a power-filled verse under all circumstances only because of who Christ is. It is not the fixing of the mind alone that brings peace. It it the character of the One on whom we fix our minds. And God does not promise to keep us in perfect peace because we have done Him the honor of trusting Him. It isn't a reward. It is an inevitable result.
Peace comes when we fix our minds on God and enter into oneness with Him and we can only do this when we know what He's like! We trust Him because we know Him. We trust Him, not because we are experts in the art of trusting, but because He is trustworthy.
"Jesus Christ the same yesterday, and today, and forever ... He is our peace ..."