Note 80 at Jn. 16:12: The Lord doesn't reveal to us things that we cannot receive. This is why we sometimes fail to get a response from God when we are petitioning Him for answers. It's not that God is unwilling to respond; it's that we are unable to receive. The way to overcome this hardness of heart (see note 3 at Mk. 8:17, p. 199) is to yield to the ministry of the Holy Spirit that Jesus begins to describe in the next verse.