There is a passage which speaks of the millennium, when Jesus Christ will rule upon earth, upon David’s throne for a thousand years. But I think we can also take it and apply it spiritually to ourselves right now. It is found in the Psalms.
"The mountains shall bring peace to the people, and the little hills, by righteousness. He shall judge the poor of the people, he shall save the children of the needy, and shall break in pieces the oppressor." [Psa 72:3-4]
In the Bible, mountains can be used to represent governments. This is most clearly seen in Daniel. We see that Daniel pictures the eternal kingdom/government of Jesus Christ as a mountain.
"Thou sawest till that a stone was cut out without hands, which smote the image upon his feet that were of iron and clay, and brake them to pieces. Then was the iron, the clay, the brass, the silver, and the gold, broken to pieces together, and became like the chaff of the summer threshingfloors; and the wind carried them away, that no place was found for them: and the stone that smote the image became a great mountain, and filled the whole earth." [Dan 2:34-35] "And in the days of these kings shall the God of heaven set up a kingdom, which shall never be destroyed: and the kingdom shall not be left to other people, but it shall break in pieces and consume all these kingdoms, and it shall stand for ever. Forasmuch as thou sawest that the stone was cut out of the mountain without hands, and that it brake in pieces the iron, the brass, the clay, the silver, and the gold; the great God hath made known to the king what shall come to pass hereafter: and the dream is certain, and the interpretation thereof sure." [Dan 2:44-45]
There are other places where mountains are used this way, but mountains do not always represent this. A lot of the time it is simply literal, a mountain. Always assume The Bible speaks literally unless it tells you otherwise. Here in Psalm 72, we can see it is symbolic, for the mountains are personified as bringing peace; thus, The Holy Spirit signifies to us a symbolic use.
What God I think has shown me with this short passage is that when you let the government of Jesus Christ rule your life it brings peace and righteousness and joy in the Holy Spirit. These are the attributes of his kingdom. Paul says in Romans, “for the kingdom of God is not meat and drink; but righteousness, and peace, and joy in the Holy Ghost.” And here in the Psalms, David tells us that The Lord will save us and break in pieces whatever is oppressing us. He will crush what oppresses us in pieces and give us freedom in Jesus!
The oppression is from sin, and freedom is found in Jesus Christ alone. Jesus Himself says,
"Verily, verily, I say unto you, Whosoever committeth sin is the servant of sin. And the servant abideth not in the house for ever: but the Son abideth ever. If the Son therefore shall make you free, ye shall be free indeed." [Jn 8:34-36]
Through Jesus Christ, victory over sin is possible. Through The Holy Spirit, oppressive sin in our life can be flattened/destroyed. Remember what The LORD tells us in Zechariah,
"…This is the word of the LORD unto Zerubbabel, saying, Not by might, nor by power, but by my spirit, saith the LORD of hosts. Who art thou, O great mountain? before Zerubbabel thou shalt become a plain: and he shall bring forth the headstone thereof with shoutings, crying, Grace, grace unto it." [Zech 4:6-7]