Being only 6 verses Chapter 12 is the smallest of Isaiah’s writings but nonetheless, important. It is a song or expression of Thanksgiving to God.
It begins with thanking God for not destroying the nation of Israel in its entirety, even though their constant disobedience warranted it. Reminding the remnant that God is their strength and salvation, the spring from which they draw life.
And in that day – Repeated from v.1, specifically referring to the time when the remnant of Israel and the chosen of the Gentile have been gathered together.
shall ye say, – better put maybe to sing out loud or louding proclaim
Praise the Lord, – what we should all be readily be doing
call upon his name, first thing each morning, that He alone will control and Glory in the day’s proceedings
declare his doings among the people, – This is the Great Commision the duty of every true believer
make mention that his name is exalted. – Again a better or more accurate translation from the Hebrew would be ‘to cause His name to be remembered forever.’
Isaiah speaks of a future event in that day, I would argue that day is here. By that I mean Why not today being the day that we:
Praise the Lord
Call Upon His Name
Declare His doings to all the earth
Cause His name to be remembered forever