Deeper Commentary

Psa 133:1

A Song of Ascents. By David-
Or 'degrees'. Hezekiah’s response to being granted another 15 years of life was to edit and produce the Songs of Degrees, so named after the degrees of the sundial. Four of the 15 Psalms were by David, one by Solomon; and the other 10 it seems Hezekiah wrote himself but left anonymous. These ten Psalms would reflect the ten degrees by which the sun-dial went backwards. The point to note is that Hezekiah taught others in an anonymous way in response to the grace he had received. True preaching reflects a certain artless selflessness. These songs of ascents were presumably also intended to be sung by the exiles as they returned to Zion, and then every time they went up to Jerusalem to keep a feast. But there is no evidence this happened. For they didn't return in the kind of faith implied in these Psalms. The plural "ascents" would then be an intensive plural referring to the one great ascent, to Zion. Much of the language of these Psalms is typical of David's language when under persecution by Saul. But the Psalm was reapplied to Hezekiah, and then to the exiles on their return from Babylon, and then by extension to all God's people on their journey zionwards.

See how good and how pleasant it is for brothers to live together in unity!-
The songs of degrees or ascents were sung by the people as they ascended in unity to keep the feasts in Zion. This unity will now be likened to the anointing oil upon Aaron (:2), and the dew (:3). Dew and oil were symbols of the blessing of the Spirit (2 Sam. 1:21). This alone is the basis for true unity. 

Psa 133:2

It is like the precious oil on the head, that ran down on the beard, even Aaron’s beard; that came down on the edge of his robes-
We note the internal agreement of the Biblical text; the oil was "poured" upon Aaron, so much so that it ran down his beard; but only sprinkled on the priests (Ex. 29:7; Lev. 8:12; 21:10). Aaron the High Priest is here likened to the whole community of Israel. They were all anointed, they were united "in him" by the oil of the spirit, looking ahead to the idea of the body of believers being "in Christ", the anointed one, the High Priest.

Psa 133:3

like the dew of Hermon, that comes down on the hills of Zion-
"Hills" may be an intensive plural for the one great hill of Zion, the temple mount. The Bible records things at times as they were perceived, even if they were scientifically wrong; the language of demons in the New Testament is an example. And here we have the myth that the dew of Hermon came down as rain in the Jerusalem area. But the idea is that as Hermon and Zion were part of the same water cycle, so the keeping of the feasts was to be a sign of unity between the north and the south. This received a small fulfilment in Hezekiah's time, whose feasts were attended by the faithful in the northern Kingdom, mingling in unity with the faithful in Judah. "Comes down" is the word used in :2 of the coming down of the oil on Aaron's beard.

For there Yahweh gives the blessing, even life forever-
This may have been the potential at the time of the restoration or even possibly in Hezekiah's time. But the preconditions weren't met, and the whole scenario has been rescheduled and reapplied to the gift of eternal life from the Lord Jesus when He sits in judgment upon David's throne in Zion. This idea of receiving the blessing of eternal life in Zion is sure evidence that the Old Testament teaches conditional rather than inherent immortality. "Life forever" is to be given in the future, at a specific location; and not at death, nor as part of any "immortal soul". The blessing of life was part of the old covenant (Dt. 30:19). But here, "life forever" is the promised blessing, implying that a new covenant [different from the Mosaic covenant] was to be entered which gave life eternal.