John Calvin Commentary Isaiah 28:11

"Nay, but by [men of] strange lips and with another tongue will he speak to this people;" — Isaiah 28:11 (ASV)

For with stammering lips. Some suggest that it means, “it is as if one were to say”; but that is unnecessary. I therefore view these words as relating to God, who, as the Prophet tells us, became a barbarian to a people without understanding. This reproof must have wounded them deeply, because by their own fault they made God, who formed our tongues, appear to be “a stammerer.”

He does not yet threaten them, but lays the blame on their indolence, showing that they made the proclamation of heavenly doctrine a confused noise. They did so because they willingly shut their eyes and thus derived no benefit from it. Their folly in not hearing God speaking to them is compared by the Prophet to a marvel.