In this five minute video from Prager U. Frank Pastore gives us an introduction to the question of whether we actually have free will and how the question bears on the further question of whether we also have a mind rather than just a material brain.
If we don't have free will it's hard to imagine how we could be held responsible for our actions, how praise or blame could be deserved, how we could have a duty to act in one way rather than another, and why we should pay any attention to our feelings of guilt or regret.
If all of our choices are determined then we really couldn't have chosen otherwise than we did, our choice was a product of factors outside our control - the environment in which we grew up or the genes we inherited from our forebears.
It's also very hard to see how, on materialism, we could have free will. If our choices are simply the product of chemical reactions occurring in the brain then where does the freedom fit in? It would seem that our choices would have to be determined by the laws of chemistry and physics and those laws admit of no freedom.
Thus, materialists are often determinists, but they're also often inconsistent determinists because they often give praise or blame to others, they often hold people responsible for their behavior, and they speak of moral duties that we have toward each other. Yet were they to be asked for an account of how these things could exist in a deterministic, materialistic world the response they'd give would be something along the lines of "They just do!", which, of course, is not very helpful.
A materialist, it seems to me, either has to be a determinist or, if not, they have to reassess their commitment to materialism. Otherwise they'll often find themselves living as if the materialism they advocate is actually false.