John Calvin Commentary Isaiah 41:6

"They help every one his neighbor; and [every one] saith to his brother, Be of good courage." — Isaiah 41:6 (ASV)

Every one brought assistance to his neighbor. What follows now agrees well with what precedes it, if you connect this verse with the last clause of the previous verse, “They drew near, they were assembled, every one assisted his neighbor;” so the meaning is, “Although the islands saw and knew my works, so that they trembled at them, yet they assembled in crowds to make a league among themselves.” Why?

This was so that they might encourage each other to create new gods and might confirm each other more and more in their blindness. He therefore aggravates the guilt of the Gentiles by saying that “every one assisted his neighbor;” Indeed, whoever makes careful inquiry will find that this is the source of all superstitions: that men by mutual consent darken the light brought to them from heaven.

But although the Lord here reasons earnestly with idolaters, yet he does it for the sake of the Jews, so that they may not fall into the impiety of the Gentiles or allow themselves to be turned away from God and from sincere faith. For this reason, he brings forward the ingratitude of the Gentiles, so that the Jews may not imitate it, but may remain steadfast in the true worship of God.

And said to his neighbor, Be courageous. Here we see, as in a mirror, how great the wickedness of men is, who profit nothing from considering the works of God, and are even made more rebellious, and harden themselves more and more. For they choose of their own accord to be blind and to shut their eyes against the clearest light, rather than to behold God who reveals himself before their eyes. To blindness is added rage, as a consequence of which they rise up against God and do not hesitate to wage war with him for defending their superstitions, so that this vice is not idol worship but idol madness. Isaiah describes this madness by saying, “Be bold, act courageously;” for he means that men have entered into a vile conspiracy, by which they naturally encourage and incite each other to the worship of idols, and to drive away the fear of God which his power might have led them to entertain.