Psalms 46:4-5
There is a river whose streams make glad the city of God,
the holy habitation of the Most High.
God is in the midst of her; she shall not be moved;
God will help her when morning dawns.
Here is another place in the Psalms where we read about 'the city of God' and something of its glories. The psalmist is referring to Jerusalem and calls it God's 'holy habitation'. It's where God lives. This fits with one of the commands of God given just before Israel entered the Promised Land.
But you shall seek the place that the Lord your God will choose out of all your tribes to put his name and make his habitation there.
God has placed His Name in Jerusalem. It is His holy habitation. Because of God's presence in her, Jerusalem 'shall not be moved'. Because God is determined to help her, she will stand victorious against all her enemies.
Now, that's all well and good, but why should we care? Are we to be terribly interested in some city in modern Israel because of what we read here? Actually, no. As with so much else in Moses and the Prophets, this is a physical picture of something that is much greater. Jerusalem is a stand-in for the Church. That's clear from a passage like this from Revelation.
And I saw the holy city, new Jerusalem, coming down out of heaven from God, prepared as a bride adorned for her husband.
John is not writing about some city in the Middle East. He writes about the Church, the Bride of Christ, which Jerusalem, the old Jerusalem, symbolized.
What this means is that we can have the same confidence that the psalmist expressed in our Psalm. God is in the midst of the Church; she shall not be moved. Or to say it using Jesus' words.
…on this rock I will build my Church, and the gates of hell shall not prevail against it.
The Church - that institution that seems so weak and is torn by division and all the rest - is a big deal. It is 'the joy of all the earth', the focus of God's work in this world. 'God is in the midst of her; she shall not be moved' until she succeeds in the work given to her: making disciples of the nations. We should be very optimistic, even when things look really bad, because of what God has promised to us, His Church.