“The sermon on the mount is a summons to follow Jesus Christ in discipleship. He alone is (the demand reaching into the depths of one’s being in which the individual instructions of the sermon on the mount are condensed and united: Matt. 5:48). On our own we cannot be perfect, as our heavenly Father is perfect – but we must be to correspond to the task our nature lays upon us.
We cannot do this, but we can follow him, cling to him, become his. If we belong to him as his limbs or members, then through our participation we become what he is: his goodness becomes ours. What the father says in the parable of the prodigal son is realized in us: All that is mine is yours (Luke 15:31).
The moralism of the sermon on the mount that is all too stiff for us is brought together and transformed into communion with Jesus, into being a disciple of Jesus; in clinging fast to our relationship to him, in friendship with him and in confidence in him.”
~Joseph Cardinal Ratzinger