What does Psalm 50:5 mean?

Prior verses called on all of heaven and earth to observe God's judgment (Psalm 50:1–3). The prior verse notes that this verdict is pronounced on God's people, the nation of Israel (Psalm 50:4; Exodus 6:7).

Courtroom trials often include a defendant who is charged with a violation of the law. In this verse the defendants are identified as having made a covenant with the Lord. When Moses explained God's covenant to Israel, the people universally agreed to follow all of God's words (Exodus 24:3). The next morning, Moses constructed an altar and made offerings to the Lord, and the people once again committed themselves to the covenant agreement (Exodus 24:4–8). Referring to this history establishes part of God's coming accusation against Israel (Psalm 50:16–17).

The description of God's people as "faithful" is deliberately ironic. The Old Testament is filled with examples of Israel turning away from the Lord's will despite His blessings and warnings (Exodus 32:7–8; Numbers 14:1–4; Judges 2:16–19). In this psalm, however, the complaint is that Israel is merely "faithful" in that they perform hollow, insincere rituals. They defy God's will and wallow in sin, but still go through the motions of religion (Psalm 50:16–21).