Psalm 121 is a “song of assent” this means it was sung while Israelites traveled, most likely when they were making their pilgrimage to Jerusalem to worship and honor God. The road to Jerusalem was rough and could be dangerous – singing this song reminded the Israelites that no matter what God was present, with them. God was leading/guiding and protecting them. When I have found myself on rough roads, this Psalm has been a source of courage and comfort. When things are rough/painful/hard/challenging/ difficult we needed to be reminded (and perhaps even sing) that God is still God and God is still good.