Here is Krauth’s illustration that explains the Lutheran understanding of Baptism as it is presented in the Augsburg Confession:
The washing of Naaman (1 Kings 5:14) in the Jordan, may be considered a foreshadowing of the baptismal idea. A promise was given to Naaman, to wit, that his leprosy should be healed. This promise was conditioned upon the presupposed faith of Naaman, but this faith was not sufficient; a mean was appointed for the fulfillment of the promise, and faith in the mean was as absolutely prerequisite in Naaman as faith in the promise. Faith in God always involves faith in His means as well as faith in His promises. If Naaman had not believed the promise he would not have gone to the Jordan; but in Naaman had believed the promise, and had yet refused to go and wash–which was the attitude he actually assumed as first–he would not have been saved from the leprosy.
The washing of Naaman was not an arbitrary association, but was made of God a real and operative mean, so that in, with, and under the water, the divine power wrought which healed his leprosy. Naaman was bound to the means, so that no element but water–no water but that of the Jordan–would have availed to cleanse him. His faith would not cleanse him without the water. Abana and Pharpar, and every river that rolled, and every sea that lifted its waves, would have rolled and risen in vain, for the water that was to do such great things was not mere water, but that water which God had enjoined, and with which his promise was bound up (Luther: Small Catechism). Yet if Naaman, earnestly striving to reach the Jordan after the promise, ad been providentially prevented, we may believe that God would have wrought the cure without the means.
Charles Porterfield Krauth
The Conservative Reformation and Its Theology