St. Teresa of Avila lived it and taught it several centuries ago. Mother Teresa lived it and taught it several years ago:
the fruit of prayer is a deepening of faith
the fruit of faith is love
the fruit of love is service
the fruit of service is peace
A clean heart. A heart free of selfish clingings. A heart unencumbered by disordered attachments. A heart beating in unison with the Sacred Heart of Jesus. It all begins with prayer.