Psalm 121 discusses how God is a constant source of help and protection. It states that God created the heavens and earth and will not fail to help those who call on Him. God is always ready to answer prayers and care for people, as He never slumbers or sleeps. The passage promises that God will protect people from dangers by day and night, and preserve their soul by helping them resist evil and walk the righteous path. The overall message is that God can be trusted to always be available to help.