What important theological issue did the Nicene Creed address?

It addressed the nature of Christ's divinity.

Explanation:

The Nicene Creed (also known as Nicaeno-Constantinopolitan Creed) is a well-known statement of belief used in Christian church. It focus on the nature of Christ (divinity and humanity), how Jesus Christ is fully and completely human and divine, and how these natures are also distinct.