1 And in that day thou shalt say, “O LORD, I will praise Thee: though thou wast angry with me, Thine anger is turned away, and Thou comforted me.
2 “Behold, God is my salvation; I will trust, and not be afraid: for the LORD JEHOVAH is my strength and my song; He also is become my salvation.”
3 Therefore with joy shall ye draw water out of the wells of salvation.
The Jews were much better about serving God and only God after the captivity. To be sure, by the time of Christ the leadership had fallen into the traps of power and greed (self-worship), but the common people mostly followed God from the return on.
And Jesus is cause enough to celebrate.
4 And in that day shall ye say, “Praise the LORD,” call upon His name, declare His doings among the people, make mention that His name is exalted.
We are to talk about God to everyone we meet, praise Him all the time.
5 Sing unto the LORD; for He hath done excellent things: this is known in all the earth.
6 Cry out and shout, thou inhabitant of Zion: for great is the Holy One of Israel in the midst of thee.
Our job, our occupation in God's kingdom is to praise Him.