C. F. Keil and Franz Delitzsch on Isaiah 40:18

Isa 40:18

The conclusion drawn from Isa 40:17, that Jehovah is therefore the matchless Being, shapes itself into a question, which is addressed not to idolaters, but to such of the Israelites as needed to be armed against the seductive power of idolatry, to which the majority of mankind had yielded. “And to whom can ye liken God, and what kind of image can ye place beside Him!” The ו before ואל is conclusive, as in Isa 28:26, and the futures are modi potent.: with what can ye bring into comparison (אל as in Isa 14:10) El, i.e., God, the one Being who is absolutely the Mighty? and what kind of demūth (i.e., divine, like Himself) can ye place by His side?