John Calvin Commentary Isaiah 60:19

"The sun shall be no more thy light by day; neither for brightness shall the moon give light unto thee: but Jehovah will be unto thee an everlasting light, and thy God thy glory." — Isaiah 60:19 (ASV)

And thou shalt no longer have the sun for the light of days. He teaches that the prosperity of the Church will not be temporary, but permanent. He distinguishes it from the ordinary condition of men, where nothing is steadfast or permanent. This is because everything under the sun, however well-regulated, is subject to various changes.

But we should not judge the Church by the dangers of the present life, for she is preserved in the midst of the billows. It is as if he had said, “Do not judge your safety from the present appearance of things, but know that it is laid up in God. God will be your sun, so that you have no need of borrowing light from the sun or the moon. Therefore, do not dread any change or revolution of affairs, for you will have a perpetual and unchangeable light.”

By these words the Prophet does not mean that the children of God will be deprived of the ordinary advantages of life. For, since the Lord bestows them indiscriminately on all men, He certainly has appointed them also for His children, for whose sake, indeed, God created all things, since He exercises special care over them. But the Prophet intended to express a still greater blessing, which the children of God alone enjoy—namely, the heavenly Light, which ungodly men hate and therefore cannot receive. For although they enjoy the sun and other blessings, yet their happiness cannot be firm and enduring, because, lacking appreciation, they do not relish what was of the greatest importance: that they have God for their Father.

Thus he distinguishes the condition of the Church and of believers from the ordinary lot of men, so that we may not judge it by the revolution and change of events, and also so that we may know that, in the midst of the thickest darkness, the fatherly kindness of God shines on believers to cheer them. And indeed, although all the elements either cease to discharge their duty or threaten us with a melancholy aspect, yet it should be enough that God is reconciled to us. By a figure of speech, in which a part is taken for the whole, he includes, under the terms “Sun” and “Moon,” the whole condition of man, which is continually undergoing change.