What does Psalm 50:15 mean?

In this psalm, the Lord has rejected Israel's sacrifices (Psalm 50:7–9). These are the very rituals God commanded them to obey (Exodus 29:38–42). The problem is that Israel performs these sacraments in hypocrisy. In the prior verse, God began to explain what is wrong with Israel's approach to sacrifices and offerings (Psalm 50:14), pointing out that they were meant to be offered with thankful, sincere hearts.

The Old Testament covenant between God and Israel included promises tied to the people's obedience (Deuteronomy 30:15–20). That dynamic is repeated here, as the Lord promises to reward those who worship Him from the heart and obey His commands. The reward is rescue from ultimate disaster, which in turn leads to God's glory.

King Hezekiah trusted in the Lord. Assyrian forces laid siege to Jerusalem and their general sent a threatening note demanding surrender. Hezekiah entered the temple and laid the letter before the Lord. He called upon Him as the sovereign God of heaven and earth (Isaiah 37:14–20). He prayed, "So now, O Lᴏʀᴅ our God, save us from [Sennacherib's] hand, that all the kingdoms of the earth may know that you alone are the Lᴏʀᴅ" (Isaiah 37:20). God answered Hezekiah's prayer by dispatching the angel of the Lord to slay vast numbers of the Assyrian army, sending the rest scurrying home (Isaiah 37:36–37).