Faith comes by hearing and hearing by the word of God.
Therefore the word of God is the only means of faith.
Therefore, where there is no word of God, there can not be any faith.
And where the word of God is, faith is entire dependence upon that word for the accomplishment of what that word says.
From all this, which is the truth, it is perfectly plain that in order for anyone to ask in faith, he must first of all be sure that he has the word of God for what he asks.
Having the word of God for what he asks, he, like David, can find it in his heart to pray with perfect confidence, which is only in perfect faith.
He who thus prays knows that he is asking according to the will of God; for he knows that he has the plain word of God for it.
Therefore he knows that God hears him; and knowing that God hears him, he knows that he has the thing for which he has asked; because the sole basis of his hope for it is the word which has spoken it, and which is the sole basis of his asking.
The Lord tells us thus to pray; and thus he has made provision for the steady, strong, and continuous growth of faith.
Many people pray, but do not know whether it is the will of the Lord that they should have what they pray for, and so do not know whether they can certainly claim it; and not knowing whether they can claim it, they are all at sea as to whether their prayers are answered or not.
The Lord does not want anybody to move uncertainly. Therefore, he has given his word, which thoroughly furnishes every one unto all good works, and by which are given all things that pertain unto life and godliness.
And any one who seeks in the word of God the things which God has there provided for all, and upon that specific word prays for that thing, thus asking according to the plainly expressed will of God, knows that his prayer is heard, and that he has the thing for which he prayed.
So doing, the prayers will be always certain, the life will be filled with the direct gifts of God, and the faith will be sure and strong, and will be ever increasing in strength.
Many pray the prayer of the disciples, "Lord, increase our faith." This is well. Yet along with this, it must never be forgotten that faith comes only by the word of God. Therefore, as certainly as your faith shall be increased, it can be only by there being in you an increase of the word of God. And the only way that there can be in you an increase of the word of God, is by your harkening to that word, praying to the Lord for the thing which that word says, depending wholly upon that word for that thing, and thanking him that you have received it. Then and thus that word is received by you, and lives in you.
Thus while we can pray, "Lord, increase our faith," at the same time we must remember that we are to build up ourselves on our most holy faith. Jude 20.
This is how to exercise faith. Faith can be exercised only on the word of God, and by the word of God; for where there is no word of God, there can not be any faith.
And "understanding how to exercise faith, this is the science of the gospel."