The Valley of Baca is also called the Valley of Weeping or the Valley of Tears. It likely symbolizes the sadness that lonely pilgrims felt (see Psalm 23:4), rather than a real place.
spring … autumn rain: Even when pilgrims feel completely worn out, the hope of getting closer to the Lord encourages them (compare Isaiah 35:6–10; 41:18–20; 43:17–20; 49:10).