Albert Barnes Commentary Psalms 84:4

"Blessed are they that dwell in thy house: They will be still praising thee. Selah" — Psalms 84:4 (ASV)

Blessed are they that dwell in your house—who are constantly there; whose permanent abode is there. The reference is to the priests and Levites—the ministers of religion—who had their permanent abode near the tabernacle and the temple, and who were wholly devoted to the sacred duties of religion. Their lot is described here as a blessed or happy one, in contrast to those who only had the opportunity of occasionally going up to worship. Compare the notes at Psalms 65:4.

They will be still praising you—They will do it constantly, as their daily employment. It will not be worship begun and ended, but worship continued—the regular business from day to day. Such will heaven be, and this will constitute its glory. There will be:

1. A permanent residence there: Him that overcometh will I make a pillar in the temple of my God, and he shall go no more out (Revelation 3:12); and
2. The constant service of God, such a service that it may be described as perpetual praise.

The Septuagint and the Latin Vulgate render this, “They will praise you for ages of ages;” that is, forever.