Psalm 136 is a song of praise, and each verse ends with the refrain "for his loving kindness endures forever." This refrain emphasizes the steadfast love and mercy of God.

Specifically, Psalm 136:20 mentions "Og king of Bashan." Og was a powerful Amorite king defeated by the Israelites as they journeyed towards the Promised Land (Numbers 21:33-35).

Here's a breakdown of the verse's meaning:

"Og king of Bashan": This refers to a historical figure who was an enemy of the Israelites. He represented opposition and a challenge to God's people. He was known for his size and strength.
"for his loving kindness endures forever": This is the key to understanding the verse. Even in the context of overcoming a powerful enemy like Og, the verse emphasizes that God's hesed (loving-kindness, steadfast love, mercy, covenant loyalty) is eternal and unwavering.

So, the combined meaning suggests:

God's power is demonstrated by His victory over formidable enemies like Og.
This victory, like all of God's actions, is motivated by and a demonstration of His enduring love and faithfulness to His people.
Even in the face of seemingly insurmountable odds, God's hesed remains constant and provides hope and assurance.

In essence, the verse uses a historical event of victory to illustrate the enduring nature of God's love and covenant commitment. It's a reminder that God's love is not dependent on circumstances; it persists even when confronting opposition and challenges. God's people can trust in His unwavering love and faithfulness, regardless of the obstacles they face.