"Happy are those who dwell in your house, they will still praise you, Selah. Happy is the one who has strength in you, who has set their heart on pilgrimage. As they pass through the Valley of Baca, they make it a place of springs; the autumn rains also cover it with pools. They go from strength to strength, till each appears before God in Zion."
The phrase "Valley of Baca" refers to the valley of tears, which is identified with the punishment of Gehenna. Rabbi Elazar said that the name "Baca" is derived from the word "be-kat," which means "lamentation." The verse teaches that even in the depths of despair, the righteous can turn their tears into springs of joy. Rabbi Yochanan said that the phrase "they go from strength to strength" means that the righteous ascend higher and higher, until they reach a level where they can praise God with the highest possible praise.
This is contrasted with those who think they are better than others, who instead of praising God, curse Him. Rabbi Yochanan said that the saying "they will still praise you" means that even after the righteous have reached the highest level of praise, they will continue to praise God, because they know that there is always more to learn and more to praise.