How sound is the Hadith which mentions the sea and the angels seeking permission to drown and destroy the son of Adam, and God's refusal to them, then His explanation of His grace and generosity towards His servants, His urging them to repent and draw closer to Him, and His mention of His treatment of the people of His obedience and disobedience?

This lengthy Hadith is not authentic. Al-Albani mentioned that, in his opinion, attributing such a long Hadith to Ahmad in his Musnad is a mistake, and it bears signs of Isra'iliyyat (stories from Jewish traditions). However, the meanings conveyed in this narration are good. Some of its contents may be supported by the saying of Allah Almighty in the Hadith Qudsi: "If he draws near to Me by a handspan, I draw near to him by a cubit. If he draws near to Me by a cubit, I draw near to him by an arm's length. And if he comes to Me walking, I come to him at speed."