Why can't a synthesis of understanding between ones will and grace be held? What that means is that through our will we choose to be Free, and through Grace we realize it? It is "not of ourselves", in the sense of the ego-seeking mind 'accomplishing' it, but that through our will we set aside the ego-seeking mind and allow Grace to unfold within and transform the individual? So both are at play. Not one without the other.
Well...it depends on what you mean by grace.
In the very moment in which God has given free will to creation (including us), he has renounced to interfere with history. He has never interfered.
Free will means autonomy from God. A person can decide to be sinless and to do good just because they want to, not in order to obey God.