We know the principles of marriage before we are married. We know as single women that we are to be a helper for their future husband, even though they don’t know who that is, yet. We know as single men that we are meant to provide for a future wife, though we don’t know who.
In the same way, God’s people in the Old covenant knew that they were meant for God. They knew the basic pattern of their relationship with Him, and that God would provide for them through a Messiah. But they didn’t know who that was yet.
Until Jesus came and turned water to wine.
At a wedding.