John Calvin Commentary Isaiah 49:13

"Sing, O heavens; and be joyful, O earth; and break forth into singing, O mountains: for Jehovah hath comforted his people, and will have compassion upon his afflicted." — Isaiah 49:13 (ASV)

Praise, O heavens; and rejoice, O earth. Though he exhorts and encourages all the godly to thanksgiving, he also aims at confirming the promise which might have been considered doubtful. For afflictions trouble our consciences and cause them to waver so that it is not easy to rest firmly on the promises of God. In short, people either remain in suspense, or tremble, or utterly fall and even faint. So long as they are oppressed by fear, anxiety, or grief, they scarcely accept any consolation, and therefore they need to be confirmed in various ways.

This is the reason Isaiah describes the advantages of this deliverance in such lofty terms, so that believers, though they saw nothing around them but death and ruin, might sustain their hearts with the hope of a better condition. Accordingly, he places the subject almost before their eyes, so that they may be fully convinced that they will have the most abundant cause for rejoicing, though at that time they saw nothing but grief and sorrow.

Let us therefore remember that whenever the Lord promises anything, we ought to add thanksgiving, so that we may more powerfully affect our hearts. Next, we ought to raise our minds to the power of God, who exercises a wide and extensive dominion over all the creatures, for as soon as he lifts his hand, heaven and earth are moved. If the signs of his wonderful power are to be seen everywhere, he intends that there will be an eminent and remarkable example of it in the salvation of the Church.

And he wilt have compassion on his poor. By this metaphor the Prophet shows that no obedience rendered to God by heaven and earth is more acceptable to him than for them to join together and lend their mutual aid to his Church. Moreover, so that believers may not faint under the weight of distresses, before promising them consolation from God, he exhorts them to bear distresses calmly; for by the word poor he means that the Church, in this world, is liable to many calamities. Therefore, so that we may partake of the compassion of God, let us learn, under the cross and amidst many annoyances, to strive after it with sighs and tears.