Jamieson, Fausset and Brown on Psalms 84:6

6. valley of Baca--or, "weeping." Through such, by reason of their dry and barren condition, the worshippers often had to pass to Jerusalem. As they might become wells, or fountains, or pools, supplied by refreshing rain, so the grace of God, by the exercises of His worship, refreshes and revives the hearts of His people, so that for sorrows they have "rivers of delight" (Psa 36:8; 46:4).