Many on the progressive Church will claim that we cannot with certainty know God's mind. And they are right. We lack the ability to know God as He is in His essence. We have the same ability to understand God that a single cell organism has to understand a person. This lack of ability to understand is one of the reasons that God reveals Himself to us. Without God's self-revelation, we would be utterly fallen and utterly without recourse.
But what the progressives follow the truth (we can't understand God and can't know Him with certainty) with is very false. They propose that, because we can't be certain about God because we can't fully understand and know God, we should allow that God desires us to do new things or to try new directions contrary to what the Church has said that God revealed in Holy Scripture.
This is a way to void the authority of Holy Scripture and replace it with the authority of the individual. Since we can't be certain of what God wants, we can't know that God doesn't want me to (get divorced, eat too much, cheat on my taxes, spend more than I make, waste resources, have sex outside of marriage, redefine marriage, take your pick). If we can't be certain of what God wants and doesn't want, then isn't almost everything adiaphora - non-essential?
The Truth (with a Capital "T") is this. We can't know God. We can't understand God. Therefore, we are bound by what God has choosen to reveal about Himself. The record of God's Self-revelation is found in Holy Scripture as interpreted by the Tradition of the Church.
Since we can't know God we must restrict ourselves to what God has shown us.