Sing, heavens; and be joyful, earth; and break forth into singing, mountains: for the Lord has comforted his people, and will have compassion on his afflicted. — Isaiah 49:13
Blessed are the poor in spirit, for theirs is the Kingdom of Heaven. — Matthew 5:3

Author
Charles Spurgeon
Summary: The Lord’s comforts are so sweet that even heaven and earth can sing of his grace toward Zion. We too can turn the mountains of difficulty, trial, mystery, and work into occasions to praise God. His promise of mercy for the afflicted calls us to sing and rejoice. The Lord wants his people to be happy in his unchanging love, without sorrow or distrust. He cannot fail us; let us respond with the joyful worship of believing hearts.
So sweet are the Lord’s consolations that not only can the saints themselves sing of them, but even heaven and earth can join in the song. It takes a great deal to make a mountain sing; and yet the prophet gathers a remarkable choir of mountains. He wants Lebanon and Sirion to sing, along with the lofty mountains of Bashan and Moab—all of them because of Jehovah’s grace toward Zion, which is His own. Can we not also turn the mountains of difficulty, trial, mystery, and toil into occasions to praise our God? “Break forth into singing, O mountains!”
This word of promise—that our God will have mercy on His afflicted ones—contains a whole peal of bells. Hear the music: “Sing!” “Rejoice!” “Break forth into singing!” The Lord wants His people to be happy because of His unchanging love. He does not want us to be sad or distrustful; He asks us for the worship of believing hearts. He cannot fail us: why should we sigh or lose heart as though He were going to fail us? Oh, how we long for a well-tuned harp! Oh, how we long for voices like those of the cherubim before the throne!
Source: The Cheque Book of the Bank of Faith. Translation by Allan Roman.
http://www.spurgeon.com.mx/chequera/meditames/julio.pdf