What does Psalm 125:1 mean?

This is one of several songs (Psalm 120—134) used by Jewish pilgrims to Jerusalem (Deuteronomy 16:16). Mount Zion was a fortress captured by David which became his capital and the city of Jerusalem (2 Samuel 5:7; 1 Kings 8:1). The psalmist is expressing the idea that those who maintain faith in God cannot be "moved" against their will to commit sin. This would correspond to the New Testament teaching that the Lord never puts His people in a position where they must sin—there is always a moral option (1 Corinthians 10:13).

A parallel interpretation relates to Israel's frequent domination by enemy empires. God preserved the people during conquest and exile (2 Chronicles 36:17–21; Ezra 2:1). Yet they were often under the control of foreign powers such as Greece and Rome (Matthew 22:17; Luke 3:1). This meant constant pressure to conform to pagan customs and beliefs. It also involved oppression on God's chosen people (Deuteronomy 10:15). With His protection, however, Israel would endure.

Christians are secure and strong when their lives are built on Christ Jesus (1 Corinthians 3:11; 1 Peter 2:4–8). They may tremble under stress, but the Rock will never tremble under them. Jesus keeps His people as secure as any mountain (John 10:28).