Albert Barnes Commentary Jonah 4:6

"And Jehovah God prepared a gourd, and made it to come up over Jonah, that it might be a shade over his head, to deliver him from his evil case. So Jonah was exceeding glad because of the gourd." — Jonah 4:6 (ASV)

And the Lord God prepared a gourd. (The English margin correctly identifies this as a castor oil plant.) “God again commanded the gourd, as He did the whale, willing only that this should happen. Immediately it sprang up, beautiful and full of flower, and at once was a roof to the whole booth, and anointed him, so to speak, with joy, with its deep shade. The prophet rejoiced at it greatly, as being a great and praiseworthy thing. See now in this also the simplicity of his mind. For he was grieved greatly because what he had prophesied did not come to pass; he rejoiced greatly for a plant. A blameless mind is easily moved to gladness or sorrow.

You will see this in children. For as people who are not strong easily fall if someone gives them no very strong push, but touches them, as it were, with a lighter hand, so too the guileless mind is easily carried away by anything that delights or grieves it.”

However little the shelter of the castor oil plant was in itself, Jonah must have looked upon its sudden growth as a fruit of God’s goodness towards him (as it was). He then perhaps went on to think (as people do) that this favor from God showed that He meant, in the end, to grant him what his heart was set upon.

Those of impulsive temperaments are constantly interpreting the acts of God’s Providence as bearing on what they strongly desire. Or again, they argue, ‘God throws this or that in our way; therefore He means us not to relinquish it for His sake, but to have it.’ By this sudden miraculous shelter against the burning Assyrian sun, which God provided for Jonah, He favored his waiting there.

So Jonah may have thought, interpreting rightly that God willed him to stay, but wrongly why He willed it so. Jonah was to wait, not to see what he desired, but to receive and be the channel of the instruction that God meant to convey to him and through him.