The first sentence is that begins with his conscience was clear... and ends with he left all his cares to heaven. That is a common suggestion when one prays, that is, leaving all our cares to heaven. Somewhere the Bible says that we should put our problems in God's hands.
The second sentence confirms the one above. The second sentence begins "in the morning, after he had said his prayers ... "
Sometimes he whirled down the incline of a wave as if he were on a hand sled.
The man is clearly in a context of desperation or at least difficulty, stuck out at sea on a life preserver. The imagery brings one of a childlike delight or a fun situation. However that is contrary to the actual situation. The man clings to a life preserver, trying to survive, not have fun, but nature rolls on, indifferent to this man's plight.
