The phrase "Praise the Lord" appears thirty-three times in the King James Bible. I find it ironic that thirty-two of them are found in the Old Testament, with its focus upon the sinfulness of mankind, and the bondage that is the Law, described as a "school-master" incapable of producing salvation. The Apostle Paul wrote:
"What then is the purpose of the law? It was added because of transgressions, till the Seed (Christ Jesus - Gen. 3:15; Gal. 3:16; etc.) should come to whom the promise was made; and it was ordained by angels in the hand of a mediator. Now a mediator is not a mediator of one, but God is one. Is the Law then against the promises of God? God forbid: for if there had been a Law given which could have given life, verily righteousness should have been by the Law. But the Scripture hath concluded all under sin, that the promise by faith of Jesus Christ might be given to those who believe. But before faith came, we were kept under the Law, ignorant of the faith which should afterwards be revealed. Wherefore the Law was our school-master to bring us unto Christ, that we might be justified by faith. But after that faith is come, we are no longer under a school-master" (Gal. 3:19-25 - SLV).
The only place "Praise the Lord" is found in the New Testament, is in Romans 15:11, which says, "And again, Praise the Lord, all ye Gentiles; and laud Him, all ye people." You would think that with the focus of the New Testament being Christ's fulfillment of the Law so that all who place their faith in His death, burial, and resurrection (all according to the prophecies found in the Scriptures - Lk. 24:25-27, 44-47; Jn. 18:32; Act. 3:18; Rom. 1:16; 1 Cor. 15:2-4; etc.) would be saved! The New Testament proclaims that salvation is a gift, accepted by faith, and not the results of works (Rom. 5:15-18; 6:23; Eph. 2:8-9; etc.)! As a result, we can join the heavenly host in praising the Lord!
"And I beheld, and I heard the voice of many angels round about the throne and the beasts and the elders: and the number of them was ten thousand times ten thousand, and thousands of thousands; Saying with a loud voice, Worthy is the Lamb Who was slain to receive power, and riches, and wisdom, and strength, and honor, and glory, and blessing. And every creature which is in heaven, and on the earth, and under the earth, and such as are in the sea, and all that are in them, heard I saying, Blessing, and honor, and glory, and power, be unto Him Who sits upon the throne, and unto the Lamb forever and ever. And the four beasts said, Amen. And the four and twenty elders fell down and worshipped Him Who lives forever and ever." (Rev. 5:11-14 SLV)!