3 You will keep in perfect peace
those whose minds are steadfast,
because they trust in you. (Isaiah 26:3 NIV)
To maintain a steadfast mind we must keep our focus upon a goal. Otherwise our minds tend to drive to a million different things. Thus, we begin with the end in mind so that we might strive always for the goal.
With this steadfast goal in mind and total focus we can find peace. If that goal happens to be God then we can put all our trust in Him and find perfect peace.