First Occurrence of "Sea of Forgetfulness" in Christian Literature Apparently "Sea of Forgetfulness" is a well known example of Christian jargon.  This is news to me, as I have never heard this phrase before today (perhaps because I am relatively young, and this phrase was more prevalent among the older generations).  The phrase appears to be an embellished derivative of Micah 7:19, "You will cast all our sins into the depths of the sea."

I am curious to know when the first instance of this phrase occurred, specifically in the Christian sense.



Here is a graph of instances of the phrase, using Google's Ngram viewer.  The first spike appears around 1817.  This might be an artifact resulting from the algorithm, however. (Google's literary database only extends from 1800 to today, with a highly irregular sample rate)
The first published use of this phrase can be attributed to Cardinal Pole, in a speech given to the English Parliament in 1554, regarding England's return to Roman Catholicism under Queen Mary:


  This I protest before you, my commission is not of prejudice to any person. I come not to destroy, but to build: I come to reconcile, not to condemn: I am not come to compel,
  but to call again: I am not come to call any thing in question already done, but my commission is of grace and clemency, to such as will receive it. For touching all matters that be past, they shall be as things cast into the sea of forgetfulness.


The speech was recorded and published in 1555, but the rise to fame of "sea of forgetfulness" can be attributed to the speech being reprinted in the first edition of Foxe's Book of Martyrs, published in 1563.  

The influence of Foxe's work was huge: it was placed alongside the Bible in many English churches in the 16th century, and was republished in many forms over the following centuries.  As one of the most popular works in the early English-speaking Protestant world, it's not surprising that this phrase would be picked up and used widely.



The original text in Foxe's work can be found in this critical edition.  The critical apparatus notes Foxe's source for the text.  

There's also an early 18th century edition, and many cleaned up text versions.  The speech is also recorded in histories of the English parliament.