Ezra 3:11 And they sang together by course in praising and giving thanks unto the Lord; because he is good, for his mercy endureth forever toward Israel. And all the people shouted with a great shout, when they praised the Lord, because the foundation of the house of the Lord was laid.
This common refrain is a promise: “The Lord will be good to His people, and His faithful love will never fail you.” Finally, God’s people came back to Jerusalem from exile in Babylon under Ezra’s leadership, and by faith they laid the foundation of the temple. This was a monumental achievement by the Lord and a great moment of glory. The event caused stupendous rejoicing among the people, and they shouted extremely loudly in giving praise and thanks to God. It sounds like you would have heard a deafening roar if you had been there.
The moment that caused the exuberant praise was the laying of the temple foundation, but the underlying cause for the grand celebration was the evidence and conviction (faith) of the goodness of God, His faithful love, and His eternal mercy. This is why we rejoice by giving thanks. God is something worth getting excited about. We could never be loud enough or get truly excited enough to really give the Lord the praise and thanks He deserves. Until we join the heavenly throng.
How do we rejoice? By thanking God. How do we thank? With exuberance. Why do we rejoice and give thanks? Because He is faithful to His covenant promises. He promises to be good to us, all the time, no matter what. The Lord keeps His promises: to love us beyond our comprehension, to be kind beyond belief, and to be faithful to the end and far beyond. And so we “give thanks unto the Lord.”