Whatever you believe about God matters a lot, because it'll impact how you live your life. Theology is simply the study of God. The more you study about God, then the more you'll know and understand about God, his character, his nature, and his dealings with mankind. The more you know, then the more you'll be better equipped to make better choices in life.
Theology matters because it greatly impacts how we live our lives.
If you have bad theology (meaning you believe the wrong things about God) you could make decisions that are potentially detrimental to you or those around you. But if you have good theology (meaning you believe the right things about God) then you are more likely to make good decisions in life and, more importantly, you are more likely to embrace all of life's circumstances with a Christ-honoring perspective.