Heidelberg Catechism 129
Q. What does the word “Amen” signify?
A. “Amen” signifies, it shall truly and certainly be: for my prayer is more assuredly heard of God, than I feel in my heart that I desire these things of him
[W]e must begin with the end, that is, we must first consider the answer to prayer. We may be surprised at this, for, from a logical standpoint, we should ask first, “What is prayer?” And only afterward, “Do we receive an answer when we pray?” Now for the Reformers the basic and vital point is this certitude: God does answer prayer. That is the first thing we must know. Calvin says it explicitly: We obtain what we request. Prayer is grounded upon this assurance. Let us approach the subject from the given fact that God answers. God is not deaf, but listens; more than that, he acts. God does not act in the same way whether we pray for not. Prayer exerts an influence upon God’s action, even upon his existence. This is what the word “answer” means.
In Question 129 of the Heidelberg Catechism it is stated that the answer to our prayer is more certain than our awareness of the things that we request. It seems there is nothing more sure than the feeling of our desires, but this Catechism says that God’s answer is still more certain. We too must have this inward assurance. Perhaps we doubt the sincerity of our prayer and the worth of our request. But one thing is beyond doubt: it is the answer that God gives. Our prayers our weak and poor. Nevertheless, what matters is not that our prayers be forceful, but that God listens to them. That is why we pray….
Let our prayer not be offered according to our good pleasure; otherwise there would be then on our part inordinate desires. Let it be patterned after the rule [the Lord’s prayer] given by the One who knows our needs better than we ourselves. God has directed us first to submit ourselves to him in order that we may present our requests. So that we may conform to this order, we must eliminate in our prayers all questions like this: Does God listen to us? On this point Calvin is categorical: “Such a prayer is not a prayer.” Doubt is not permitted, for it goes without saying that we shall be heard. Even before we pray we must assume the attitude of someone who has been heart….
“Amen.” It is enough to recall what Luther and the Heidelberg Catechism tell us about this. Luther affirms that it is a good thing to say “Amen”! In other words, it is a good thing to learn not to doubt when we pray, but to believe, because “Amen” means, “So be it.” Prayer is not an undertaking left to chance, a trip into the blue. It must end as it has begun, with conviction: Yes, may it be so! On its side, the Heidelberg Catechism declares that “Amen” means that the certainty of the divine response is greater than the certainty we feel within ourselves of our needs and desires. The most certain element of our prayer is not our requests, but what comes from God: his response.
[Karl Barth, Prayer, 50th Anniversary Edition (Louisville, KY: Westminster John Knox, 2002). 13, 19-20, 65-66.]