This is a quote from that day. "The Hebrew reference "Yah" is also spelled "Jah". this shortened form of the covenant name "Yaweh" is employed many times in the Hebrew Old Testament. You say it every time you use the word, Hallelujah, meaning "Praise ye Jah". Here is the part I find most intriguing: "JAH is a shortened form of Jehovah..Pronounced "ya", this name signifies, HE IS, and can be made to correspond to I AM, just as Jehovah corresponds to the fuller expression I AM THAT I AM.
This is what I found in reference to the definition of Hallelujah:
Hallelujah meaning "Praise Yah". The last syllable is from the first two letters of the name of God, YHWH. the word is used a great deal in the Psalms in part of the Hallel prayers. Psalms, e.g. 111–117, 145–150, and four times in Revelation.
"hallelujah" means more than simply "praise Yah", as the word hallel in Hebrew means a joyous praise in song, to boast in God. Hallel could also refer to someone who acts madly or foolishly.
The second part, Yah, is a shortened form of YHWH, the name for the Creator. This name is not pronounced by Jews, as they do not permit the speaking of the name of God, and in any case the correct pronunciation is not known.
The word hallelujah occurring in Psalms is therefore a request for a congregation to join in praise toward God. It can be translated as "Praise God" or "Praise Yahweh, you people", and is usually worded in English contexts as "Praise the LORD".
"Hallelujah" appears in Revelation 19, the great song of praise to God for his triumph over the Whore of Babylon.