Psalms 135, 136, 138, and 139 are Psalms of thanksgiving.
Psalm 135 is a song of praise for God’s wonderful works in nature
and in history. A nation that is now cleansed and converted worships
God in this Psalm. The call to worship is found in verses 1-4;
adoration to Him who controls nature in verses 5-7; adoration to Him
who redeemed the nation and set it in Palestine in verses 8-18; and
adoration to Him who is above all gods and therefore worthy of all
worship in verses 19-21.
Psalm 136 seems to be an extension of Psalm 135 and is
continuing praise to Almighty God. Also, it is called a Hallel
Psalm, which means it was sung at the opening of the Passover and
was a favorite Temple song.
One of the great themes of the Bible is the mercy of God. In
Psalm 136 alone the word “mercy” is found 26 times, one time for
each verse. Perhaps it would be helpful for us to distinguish
between mercy and grace. They are not one and the same. One is
negative and one is positive. One keeps us from hell, and the other
assures us of heaven. Mercy is not getting what you deserve (hell
and judgment), while grace is getting that which you do not deserve
(heaven and God’s blessing).
In Psalm 137 the Jewish captives hung their harps on the
trees beside a river near Babylon and sat down and wept. They had
been captured by the enemy for their disobedience. But even in
captivity they would trust that God’s mercy would not forsake them.
And they would not be let down.