Psalm 46 is considered as being part of a trilogy (Pss 46+47+48) of praise to God for a deliverance of Jerusalem from fierce and powerful enemies. Some scholars would connect this to something like 2 Kings 18:9–19:37, to the deliverance of Jerusalem in 701 BC from an Assyrian army. (see J. E. Smith, The wisdom literature and Psalms (Ps 46:1-48:1), College Press Pub. Co., Joplin, Mo., 1996).
The city is Jerusalem. Why?
- Because it is called "the city of God",
- Because it hosts "the dwelling of the Most High", which is the Temple, combining the two ideas of the dwelling-place and the consecrated place. BTW, "the Most High" is a divine name: ‘Elyon [עֶלְיוֹן], like in Psalm 7:17; 9:2; 21:7 etc.
As about God and His city see among various other places:
Great is the Lord and greatly to be praised in the city of our God!
His holy mountain, beautiful in elevation, is the joy of all the
earth, Mount Zion, in the far north, the city of the great King.
Within her citadels God has made himself known as a fortress. (ESV)
On the holy mount stands the city he founded; the Lord loves the gates
of Zion more than all the dwelling places of Jacob. Glorious things of
you are spoken, O city of God. (ESV)
The presence of the Lord inside of the city is securing:
Zephaniah 3:15 :
... The King of Israel, the LORD, is in your midst; you shall never again fear evil.
The river: If the city is Jerusalem, then the rivers might be some irrigation ditches or the waters of Shiloah, incoming from a spring called Gihon and going to Siloam. This is a facility built up by Hezekiah, bringing water from the Wady Urtas to Jerusalem, and distributing it into several ditches and ponds:
2 Kings 20:20 sq.:
Now the rest of the acts of Hezekiah and all his might, and how he
made the pool and the conduit and brought water into the city ...
There is a very significant fragment about this in Isaiah 8:6-8:
“Because this people has refused the waters of Shiloah that flow
gently, and rejoice over Rezin and the son of Remaliah, therefore,
behold, the Lord is bringing up against them the waters of the River,
mighty and many, the king of Assyria and all his glory. And it will
rise over all its channels and go over all its banks, and it will
sweep on into Judah, it will overflow and pass on, reaching even to
the neck, and its outspread wings will fill the breadth of your land,
O Immanuel.” (ESV)
What we got here? These waters contrasted with the flood as a symbol for Assyria. Perhaps we can draw the conclusion that these rivers convey the meaning of the peace and prosperity that the Lord provides for Jerusalem, in contrast to the chaos outside the city. It would mean the rich blessings of God's favor to His city.
We can conclude this by saying that it is all about reassuring that God's people have nothing to fear in the presence of the Lord. In contrast to the raging sea, the river is a symbol of the presence of the Lord, blessing His city / His people.
Break of day
Now what about the "break of day". In contrast, the night is a time of fear and trouble, when enemies gather around the city as a flood. Yet "morning" is a metaphor for the time of deliverance, following the night of distress.
For his anger is but for a moment, and his favor is for a lifetime.
Weeping may tarry for the night, but joy comes with the morning.
At evening time, behold, terror! Before morning, they are no more!
This is the portion of those who loot us, and the lot of those who
plunder us. (ESV)
In Exodus there is a verse that presents some symbols that we got here: the sea, the dawn ...
So Moses stretched out his hand over the sea, and the sea returned to
its normal course when the morning appeared. And as the Egyptians fled
into it, the LORD threw the Egyptians into the midst of the sea. (ESV)
Or let's just return to 2 Kings 19:32-36
“Therefore thus says the LORD concerning the king of Assyria: He shall
not come into this city or shoot an arrow there, or come before it
with a shield or cast up a siege mound against it. By the way that he
came, by the same he shall return, and he shall not come into this
city, declares the LORD. 34For I will defend this city to save it, for
my own sake and for the sake of my servant David.” And that night the
angel of the LORD went out and struck down 185,000 in the camp of the
Assyrians. And when people arose early in the morning, behold, these
were all dead bodies. Then Sennacherib king of Assyria departed and
went home and lived at Nineveh." (ESV) / (See also Isaia 37:36)
Some early Christian commentators interpreted the river as a symbol of God's providence:
John Chrysostom, Commentary on the Psalms 46.1
As a river divided into countless tributaries waters the surrounding
land, so God’s providence flows everywhere, spreading copiously,
advancing in a rush and covering everything.
See also an interesting Christian allegorical comment from about the Vth century AD:
Theodoret of Cyr, Commentary on the Psalms 46.5
He gave the name “river” here to the preaching of the gospel and
“city” to the way of life of God-fearing people, watered by the
streams of the river to the point of fruitfulness.
Last but perhaps not least, a comment from the IVth century AD, where the author is relating everything to Jesus Christ and the resurrection:
Ambrose of Milan, Commentary on Twelve Psalms 46.14
By his resurrection at dawn, the Lord confers on us wonderful and
heavenly helps. His resurrection dispelled the night and poured on us
the light of day. As Scripture says, “Rise, O sleeper; arise from the
dead, and Christ shall enlighten you.”(Eph 5:14) Consider here a
mystery. Christ suffered in the evening, and according to the Old Law,
the lamb is slain at evening (Deut 16:6). [...] In the evening of this
world, when the light is failing, he is killed (Mt 27:45). All this
world would have been shrouded by even greater and more horrid
darkness only that Christ came to us from heaven. He, the eternal
light, came to us from heaven to restore to the human race the age of
innocence. The Lord Jesus suffered, and by his blood forgave us our
sins. The light of a pure conscience shone out and a day of spiritual
grace dawned with splendor.