The God of Jacob.
The line of Jesus Christ is through Abraham, Issac, and Jacob. You can see this in the lineage of Jesus Christ in several chapters of the new testament.
As a man..from Adam..continuing on ..somewhere you find Abraham...his son Issac..and then Issac's son Jacob...Abraham's grandson....and continuing on to Jesus Christ.
The God of Jacob is one manner in which it is described..from a genealogical standpoint.
The "Lord of Hosts"..is an Olde Testament way or manner of describing the God of Abraham, Issac, and Jacob. The I am..of the Olde Testament. Jehovah is another word for God..The Lord of Hosts..and it can be spelled differently among different peoples.
Psalm 46 as are many of the Psalms are a praise to God..the God of Jacob..of Abraham and Issac.
In like manner to many of the Psalms and also other passages ..the fear of this world and death/calamity hold no sway to believers in the God of Abraham, Issac, and Jacob. For they put their Faith in God and not the things of this world.
The "River" ..I am using a King James for Psalm 46:4... is representative of God's power/blessing/mercy on His People...His Way.
Notice in 46:3 the usage of troubled waters and then "Selah"
Then on to 46:4 and 46:5
The verses are speaking from the beginning of Psalm 46 of trouble and calamity ..even troubled waters and seas..
But by the time you get to 46:4 the waters are calmed..refuge...as in 46:1
and finally to 46:5..for His people..whom He Chose.
46:1 God [is] our refuge and strength, a very present help in trouble.
46:2 Therefore will not we fear, though the earth be removed, and though the mountains be carried into the midst of the sea;
46:3 [Though] the waters thereof roar [and] be troubled, [though] the mountains shake with the swelling thereof. Selah.
46:4 [There is] a river, the streams whereof shall make glad the city of God, the holy [place] of the tabernacles of the most High.
46:5 God [is] in the midst of her; she shall not be moved: God shall help her, [and that] right early.
46:6 The heathen raged, the kingdoms were moved: he uttered his voice, the earth melted.
46:7 The LORD of hosts [is] with us; the God of Jacob [is] our refuge. Selah.
46:8 Come, behold the works of the LORD, what desolations he hath made in the earth.
46:9 He maketh wars to cease unto the end of the earth; he breaketh the bow, and cutteth the spear in sunder; he burneth the chariot in the fire.
46:10 Be still, and know that I [am] God: I will be exalted among the heathen, I will be exalted in the earth.
46:11 The LORD of hosts [is] with us; the God of Jacob [is] our refuge. Selah.
At times when I read verses which confuse me ..I know to read the verses before and after them to get the context. Sometimes several verses before and after.
The word Selah..is a connective...often used in the Hebrew technique of connecting or rhyming thoughts ..not verses as is popular in the west.
Hope this helps some of you.