In Psalm 55, David testifies that the LORD hears his prayer. He is right to call to him for help, morning and evening and he knows what it is to live in dependence on God. This will be a good song to sing in response to your sermon, especially those stanzas that speak to the LORD hearing and answering prayer.
5 “And when you pray, you must not be like the hypocrites. For they love to stand and pray in the synagogues and at the street corners, that they may be seen by others. Truly, I say to you, they have received their reward.