"And when distress touches you," meaning: the terrors, "at sea, those you call upon are lost," meaning: those whom you worship, "except Him." He says: except Him you call upon, similar to His saying: "Rather, Him alone you call upon." You know that no one can save you from drowning except Him. "But when He delivers you to the land, you turn away," from the One who saved you, and return to your polytheism. "And ever is man ungrateful," meaning: the polytheist.