In John 6: 44-51, Jesus says that "No one can come to me unless the Father...draw him/her." This means that the experience of union with God is a Gift. Our spiritual practice of centering or mantra prayer, can make us more receptive to the experience of union, but it cannot control God. A person can be suddenly enlightened, without any practice at all.
It also says in this passage of Scripture, "They shall all be taught by God." There is no intermediary teacher for the experience of God. Teachers can inform us about doctrine, which are "about God" but not God in God's immediate Self. Teachers can show us a practice of letting go of thoughts and images of God, but they cannot control God.
God is already One with us, but we just don't know it in an experiential way.