Like most errors in Bible-reading, one must fix the error by reading the scripture in context. It also helps to have read other parts of the Bible to understand the history and the significance of what is being read.
I will help you understand what you are reading.
First understand that, like many Psalms in the Bible, this one is prophetic in that it reveals what is to come and how everybody will feel about it when it happens.
The 137th Psalm is a plaintive song of the exile; of one who has recently returned from Babylon but in whose soul lingers the bitter memory of the years in a foreign land and of the cruel events that led to that enforced stay.
Verses 7-9 of this Psalm call for retribution on Edom and Babylon. It will help to have this Psalm in front of you (verses 1-9) and follow along as I clarify what you are reading:
The rivers mentioned in Verse 1 are, as you may have guessed, the Tigris and Euphrates, as well as the many canals associated with them. Over and over again, the thought of their forced separation from Zion brought them down to the posture of mourning (much like what is written in Job 2:8, 13 as well as in Lamentations 2:10).
Verse 2 spoke of the sorrowful harps (see also Isaiah 24:8 and Job 30:31). All harps were tuned to a mourning tone because of the callous Babylonians' oppression on Jerusalem.
Verses 4-6 shed light on how the poet feels about being a puppet for the Babylonians and how, only someone whose heart had disowned the Lord AND Jerusalem could possibly go along with them.
Verses 7-9 is a call from a loyal subject of the ravaged city of Jerusalem, that Babylon may suffer the same fate as the fate dealt to Jerusalem at their hands. It is no doubt a VENGEFUL tone, and one taken in a time before Jesus came to teach us how to turn the other cheek.
Lamentations 4:21 suggests that Edom will receive a similar punishment that Jerusalem suffered and, as any Bible fan knows, Edom is the subject of an agelong animosity due to the people's descendency from Esau (Jacob's brother).
In fact, many a prophet predicted the Lord's judgment against the Edomites (see Isaiah 63:1-4; Jeremiah 49:7-22; Ezekiel 25:8, 12-14; Chapter 35, etc).
And now, for Verse 9, which reads as follows:
"Happy shall he be, that taketh and dasheth thy little ones against the stones."
Meaning: Well.... war was as brutal and vicious then as it is now. Sadly, women and children were not spared the wrath of man-made warfare (see other examples at 2 Kings 8-12; 15:16; Isaiah 13:16, 18; Hosea 10:14; 13:16; Amos 1:13 and Nahum 3:10).
Further reading (to announce the final destruction of the "Babylon" that persists in its warfare against the City of God, and the JOY with which that announcement is greeted), have a read of Revelation 18:1 through Chapter 19:4.
So, like I said.... it helps to read more than just one verse if one expects to truly understand what is being read.
Hope that helps. <")))><
King James Bible and Bible study documents.