I have long time holden my peace; literally, for an eternity. God's love for his people is forcibly expressed by his saying that he has felt it "an eternity"—though it was but some five or six decades—while he was waiting for his chastisement to have such due effect as would allow of his bringing it to an end, and showing them mercy.
He has chafed, as it were, under the necessity of inaction, and has with difficulty refrained himself. Now he will refrain no longer. A travailing woman. A woman in her travail, after long endurance, at last gives free vent to her natural feelings, and utters loud cries (compare the preceding verse).
I will destroy and devour at once (so Gesenius, Kay, and the ancient versions). But the bulk of modern commentators render, "I will pant and gasp," as does a travailing woman.