The doctrine of the Church, and of the necessity of her external unity, which began to prevail so early as the third century, favoured the pretensions of Rome. The primary idea of the Church is, that it is the assembly of the saints, (1 Cor., i, 2,) the assembly of the first-born whose names are written in heaven. (Heb., xii, 23.) Still, however, the Church of the Lord is not merely internal and invisible. It must manifest itself outwardly, and it was with a view to this manifestation that the Lord instituted the Sacraments of Baptism and the Eucharist. The Church considered as external, has characteristics different from those which distinguish her as the Church invisible. The internal Church, which is the body of Christ, is necessarily and perpetually one. The visible Church, doubtless, has part in this unity, but considered in herself, multiplicity is a characteristic attributed to her in the Scriptures of the New Testament. While they speak to us of a Church of God,[9] they mention, when speaking of the Church, as externally manifested, "the Churches of Galatia," "the Churches of Macedonia," "the Churches of Judea," "all the Churches of the Saints."[10] These different Churches, unquestionably, may to a certain extent cultivate external union; but though this tie be wanting, they lose none of the essential qualities of the Church of Christ. In primitive times, the great tie which united the members of the Church was the living faith of the heart, by which all held of Christ as their common Head. [9] 1 Cor. xv, 9. 1 Tim. iii, 15. [10] 1 Cor. xvi, i. 2 Cor. viii, 1. Gal. i, 22. 1 Cor. xiv, 33.