And since we have the same spirit of faith in keeping with what is written, I believed, therefore I spoke, we also believe, and therefore speak. 2 Corinthians 4:13
Everything starts with believing. Where there is no belief there is no participation. The only time one speaks contrary to what they believe is when they engage in deception. Paul declares that his speaking results from belief. That belief came from revelation not pretension or wishful thinking. Anyone who knows of the Apostle Paul is familiar with his history: he had opposed the good news of Jesus to the point of having those who followed it put to death.
Paul's previous training was extremely rigorous and he had been convinced intellectually that adhering to the Law was the only thing that pleased God. Intellectual agreement does not stand the test when the pressure is up in the spiritual realm.
Many are discovering this today as they attempt to practice the principles being taught on healing, prosperity and the like. While the teaching may be correct it works inconsistently on an intellectual level. Like salvation, these principles function by faith. Heb. 11:1 declares that faith is assurance. Faith knows the outcome; it is revelatory belief. Perhaps the way to your answer appears to be taking a confusing route. When you are in faith, you can rest in the promise because you believe in your heart.
This does not mean that the teaching is in error. For the person who has received the Spirit's guarantee the promise has expanded from the intellect and is firmly established on solid ground. It is no longer a formula that causes you to recheck the equation when the result does not appear as quickly as desired. Faith enables you to enter the rest of God, the place of peace-filled trust. “Therefore, since the promise of entering his rest still stands, let us be careful that none of you be found to have fallen short of it. For we also have had the gospel preached to us, just as they did; but the message they heard was of no value to them, because those who heard did not combine it with faith.” (Heb. 4:1-2).