I have noted the two properties of the institutional aspect of the bond. But the bond can be either merely natural or also sacramental. The two properties apply in either case. However, the unity in the natural order is simply the spousal unity of two human beings of opposite sex. It is a unity of those who can form a proper sexual friendship. It is tender and lifelong. It is “total” as one of the good public defenders of true marriage has indicated. Yet, it is not nearly as glorious as the sacramental bond.
Of incomparably greater strength, goodness, and beauty is the sacramental unity established by Christ between a baptized man and a baptized woman. The bond of Christians who are married is a sign of the bond between Christ and the Church (Eph 5:25, 32). Just as Christ shall never leave his bride, so this sacramental bond is absolutely indissoluble.
That is, when Christians licitly marry and consummate their marriage, there is absolutely no authority on earth, neither the power of an unreligious state, nor the power of a state that, rightly following its duty, recognizes the authority of the one Church of Jesus, nor even the supreme power of the Church of Jesus herself – the Pope. No one may break what God has joined in this manner. By contrast, a merely natural marriage, even if consummated, can under certain circumstances be broken by the power of Jesus’ Church. (Note that that would not be divorce.)
In all of this, the secular authority is absolutely out of its depths. The secular authority has not anything licitly to say about any of this except insofar as it recognizes the divine appointment of the Catholic Church.