"And on the fourth day they assembled themselves in the valley of Berachah; for there they blessed the Lord: therefore the name of the same place was called, The valley of Berachah, unto this day." (2 Chronicles 20:26)
The name Berachah means "blessing," and the people of Judah surely had much reason to bless the Lord. The armies of the Moabites and Ammonites, and many others, had invaded their land, and King Jehoshaphat had no forces sufficient to oppose them.
But Jehoshaphat had already led his people back to the Lord, and now he prayed for their deliverance, acknowledging that the Lord was "God in heaven . . . so that none is able to withstand thee." Therefore God replied, through the prophet Jahaziel, that "the battle is not yours, but God's . . . stand ye still, and see the salvation of the LORD" (2 Chronicles 20:6, 15, 17). God then set the invading armies against each other, until all were slain, and God's people were delivered without even lifting a sword. No wonder the people "blessed the Lord!"
The Hebrew word berachah ("blessing") is used some 68 times in the Old Testament, the first being God's promise to Abraham, when he followed the Lord: "And I will make of thee a great nation, and I will bless thee, and make thy name great; and thou shalt be a blessing" (Genesis 12:2). God's promise to Abraham has been abundantly kept though there is much more to come. We, like the people in the valley of Berachah, have much for which to bless the Lord, for we also have seen the salvation of God: "Worthy is the Lamb that was slain to receive power, and riches, and wisdom, and strength, and honour, and glory, and blessing" (Revelation 5:12).
Therefore, "Bless the LORD, O my soul: and all that is within me, bless his holy name" (Psalm 103:1). HMM