I think that the line "For the pounding and calling at a door in your little chest" is referring to Revelation 3:20, which says "Behold, I stand at the door and knock; if anyone hears My voice and opens the door, I will come in to him and will dine with him, and he with Me."
I think that the line "For the pounding and calling at a door in your little chest" is referring to Revelation 3:20, which says "Behold, I stand at the door and knock; if anyone hears My voice and opens the door, I will come in to him and will dine with him, and he with Me."