Nahum 1:3 says the LORD is slow to anger and great in what?

Answer: Power

"The LORD is slow to anger and great in power; the LORD will by no means leave the guilty unpunished."

“The LORD is slow to anger and great in power; the LORD will by no means leave the guilty unpunished. His path is in the whirlwind and storm, and clouds are the dust beneath His feet.”— Nahum 1:3 (BSB)