My understanding is that Hallelujah (or Alleluia) is a compound word from the Hebrew ‘hallelu’, meaning “to praise joyously,” and ‘yah’, a shortened form of the unspoken name of G-d. It is an active imperative, an instruction to the listener or congregation to sing joyful praise to Hashem.
Hallelujah appears in 15 different Psalms, between 104-150, and in almost every case at the opening and/or closing of the Tehilm/Psalm. These passages are called the "Hallelujah Psalms." A good example is Psalm 113: Praise the Lord!
However, I can't help but think there is more behind the combining of these two Hebrew words; that if the heavenly, angelic hosts were to praise and worship Hashem by crying out "Hallelujah" or "Alleluia" then it would be something sacred and special, that heaven would reverberate to the concert of heavenly music, as the voice of many waters and of mighty thunderings.
May I respectfully enquire if "Praise the Lord" (as used in the Tehilm/Psalms) has a deeper, a more significant and spiritual meaning than simply singing joyful songs of praise?
I saw this related question, but it does not address my specific question: Why should other nations praise G-d because of His mercy towards us?