The Lord is my portion; I have promised to keep Your words.
Psalm 119:57

When the psalmist wrote that God was his “portion,” he was using a word that had rich meaning in Jewish religious history. When the Israelite tribes came out of the desert and made their conquest of the land of Canaan and every tribe received its appointed portion, the priestly tribe of Levi did not receive land. Instead they were given forty-eight priestly cities scattered throughout the land and were to live there so that their priestly service would always be widely available. They had no land, but they were given something better. It was said of them that they had “no inheritance [portion]” in the land because “their inheritance [portion] was the Lord” (Josh. 13:33).1

But to the tribe of Levi, Moses did not give an inheritance; the LORD, the God of Israel, is their inheritance, as He had promised to them.
Joshua 13:33

Our Lord is the portion for all true believers:

Whom have I in heaven but You? And besides You, I desire nothing on earth. My flesh and my heart may fail, but God is the strength of my heart and my portion forever.
Psalm 73:25–26

I cried out to You, O Lord; I said, “You are my refuge, My portion in the land of the living.”
Psalm 142:5

“The Lord is my portion,” says my soul, “therefore I have hope in Him.”
Lamentations 3:24

When God is our portion, we will respond the same way the psalmist did: “I have promised to keep Your words.” We can do no less when we have received the words of eternal life!

1Boice, J. M. (2005). Psalms 107–150: An Expositional Commentary (p. 1001). Grand Rapids, MI: Baker Books.