Patrick Henry Reardon gives insight into the repeated phrase "For His mercy endures forever" in the Psalms...
Psalm 135 insists, literally in every verse, that the root of all of God's activity in this world, beginning even with the world's creation, is mercy - hesed. This mercy is eternal - le'olam - "forever."
Mercy is the cause and reason of all that God does. He does nothing, absolutely nothing, except as an expression of His mercy. His mercy stretches out to both extremes of infinity. "For His mercy endures forever" is the palimpsest that lies under each line of Holy Scripture. Thus, too from beginning to end of any Orthodox service, the wor
d "mercy" appears more than any other word. The encounter with God's mercy is the root of all Christian worship. Everything else that can be said of God is but an aspect of His mercy.
Mercy is the defining explanation of everything that God has revealed of Himself. Every Orthodox service of worship, from Nocturnes to Compline, is a polyeleion [or "manifold mercy"], a celebration of God's sustained and abundant mercy. What we touch, or see, or hear, or taste - from the flames that flicker before the icons and the prayers our voices pour forth, to the billowing incense and the mystic contents of the Chalice - all is mercy.
Mercy is the explanation of every single thought that God has with respect to us. When we deal with God, everything is mercy; all we will ever discover of God will be the deepening levels of His great, abundant, overflowing, rich and endless mercy. "For His mercy endures forever" is the eternal song of the saints.
- from Christ in the Psalms
Psalm 135
Oh, give thanks to the LORD, for He is good!
For His mercy endures forever.
Oh, give thanks to the God of gods!
For His mercy endures forever.
Oh, give thanks to the Lord of lords!
For His mercy endures forever:
To Him who alone does great wonders,
For His mercy endures forever;
To Him who by wisdom made the heavens,
For His mercy endures forever;
To Him who laid out the earth above the waters,
For His mercy endures forever;
To Him who made great lights,
For His mercy endures forever—
The sun to rule by day,
For His mercy endures forever;
The moon and stars to rule by night,
For His mercy endures forever.
To Him who struck Egypt in their firstborn,
For His mercy endures forever;
And brought out Israel from among them,
For His mercy endures forever;
With a strong hand, and with an outstretched arm,
For His mercy endures forever;
To Him who divided the Red Sea in two,
For His mercy endures forever;
And made Israel pass through the midst of it,
For His mercy endures forever;
But overthrew Pharaoh and his army in the Red Sea,
For His mercy endures forever;
To Him who led His people through the wilderness,
For His mercy endures forever;
To Him who struck down great kings,
For His mercy endures forever;
And slew famous kings,
For His mercy endures forever—
Sihon king of the Amorites,
For His mercy endures forever;
And Og king of Bashan,
For His mercy endures forever—
And gave their land as a heritage,
For His mercy endures forever;
A heritage to Israel His servant,
For His mercy endures forever.
Who remembered us in our lowly state,
For His mercy endures forever;
And rescued us from our enemies,
For His mercy endures forever;
Who gives food to all flesh,
For His mercy endures forever.
Oh, give thanks to the God of heaven!
For His mercy endures forever.
things of life through the sensible faculty as if by a nail, it is hard to turn away from them. It has grown up together with these attachments much in the same way as the shellfish and snails are bound to their covering of clay; and so it is slow to make such movements, since it drags along the whole burden of a lifetime. As such is its condition, the soul is easily captured by its persecutors with the threat of confiscation of property or loss of sonic other things that are coveted in this life; and so it gives in easily, and yields to the power of its persecutor.