Behold, for peace I had great bitterness: but thou hast in love to my soul delivered it from the pit of corruption: for thou hast cast all my sins behind thy back. For peace I had great bitterness "My anguish is changed into ease" - מר לי מר mar li mar, "mutata mthi est amaritudo." Paronomasia; a figure which the prophet frequently admits. I do not always note it, because it cannot ever be preserved in the translation, and the sense seldom depends upon it. But here it perfectly clears up the great obscurity of the passage. See Lowth on the place.
Thou hast rescued - חשכת chashachta, with כ caph, instead of ק koph; so the Septuagint and Vulgate; Houbigant. See Chappelow on Job 33:18.
From perdition - משחת בלי mishshachath beli, ἱνα μη αποληται, Sept. ut non periret, "that it may not perish." Vulg. Perhaps inverting the order of the words. See Houbigant.
Thou hast in love to my soul - חשקת chashakta, "thou hast lovingly embraced" or kissed "my soul out of the pit of corruption."