What does the mariner's not being able to speak signify in "The Rime of the Ancient Mariner"?

In Part IV of "The Rime of the Ancient Mariner" by Samuel Taylor Coleridge, the Mariner tries to pray but only a "wicked whisper came, and made/My heart as dry as dust."  The Mariner had killed the albatross showing a disregard for nature; his dead men lie on the rotting deck and when the Mariner looks at the rotting sea he sees "a thousand thousand slimy things."  It is not until the Mariner watches the water snakes in their rich attire of blue, glossy green, and velvet black and enjoys their beauty "Oh happy living things! no tongue/Their beautymight declare" and a "spring of love" gushes from his hear that he can pray "And the selfsame moment I could pray/And from my neck so free/The Albatross fell off, and sank/Like lead into the seas."