What are "returning and rest" (30:15)?

The verse gives the words, and the chapter sets them against what the people chose. "For thus said the Lord GOD, the Holy One of Israel, “You will be saved in returning and rest. Your strength will be in quietness and in confidence.” You refused" (30:15), "but you said, “No, for we will flee on horses;”" (30:16). Returning is shuvah, which the Hebrew Bible has only here (tap returning). Strong's gives it as "a return", and as "from 7725", the verb shuv, return; Brown-Driver-Briggs gives "retirement, withdrawal (from war, etc., cf. Mi 2:8)". Rest is nachat, "quietness, rest" (Brown-Driver-Briggs) (tap rest). Quietness is the verb of "Be careful, and keep calm" (7:4), and confidence is bitchah, which the Hebrew Bible also has only here; Brown-Driver-Briggs gives "trusting". The chapter on Isaiah 32 sets the verse beside "quietness and confidence forever" (32:17), where quietness is the same verb and confidence is another word. The verse doesn't say what the returning is from or to, and these notes don't settle it. What the chapter sets beside it is the answer of 30:16: horses, and flight.