This subject has been treated by many writers; yet there seems to be room left for a popular exposition which addresses itself to the general public and deals with the most recent phases of the question and the position created by the definition of the Vatican Council. Professor Hettinger insists much on three fundamental ideas of Christ's kingdom, viz.: the idea of a Church, the idea of the unity of the Church, and the idea of Church government. The Church must be one, numericaBy; she must be one there may not be many churches. She must be one within herself; she must be one in faith, one in worship and one in corporate life. St: Paul describes the unity of the Church. "Careful to keep the unity of the Spirit in the bond of peace: One body and one Spirit as you are called in one hope of your vocation. One Lord, one faith, one baptism unto the edification of the body of Christ. Till we meet in the unit of faith ... That we may not now be children tossed to and fro, and carried about with every wind of doctrine ... But we may in all things grow up in Him Who is the Head, Christ." (Ephes. 4, 3-16.) All whatever differences ill nationality, language, circumstance may separate them, must be one in faith, must reject doctrines opposed to the faith and must grow up in Him Who is the Head. The unity in worship follows from the unity of faith: no act of worship may contradict the faith or fail to express it. The corporate unity, the unity of Government was established by Jesus Christ in order to preserve the unity of faith. Without corporate organic unity the unity of faith would soon perish, and the unity of worship would soon be lost. The figures under which the Church is represented in the New Testament all imply this corporate unity. She is the kingdom of heaven, a Rock under one shepherd, the vine from which every branch grows, a temple, a house, above all she is the mystical body of Christ.