Christians do not stand isolated, each holding his own creed. They constitute one body, having one common creed. Rejecting that creed, or any of its parts, is the rejection of the fellowship of Christians, incompatible with the communion of saints, or membership in the body of Christ. In other words, Protestants admit that there is a common faith of the Church, which no man is at liberty to reject, and which no man can reject and be a Christian.
It is the love of Christ, i. e. his love to us which passes knowledge. It is infinite; not only because it inheres in an infinite subject, but because the condescension and sufferings to which it led, and the blessings which it secures for its objects, are beyond our comprehension. This love of Christ, though it surpasses the power of our understanding to comprehend, is still a subject of experimental knowledge. We may know how excellent, how wonderful, how free, how disinterested, how long-suffering, how manifold and constant, it is, and that it is infinite. And this is the highest and most sanctifying of all knowledge. Those who thus know the love of Christ towards them, purify themselves even as he is pure.
In a multitude of cases, and in all cases where regeneration is spoken of, it means the whole soul; that is, it includes the intellect, will, and the conscience as well as the affections. Hence the Bible speaks of the eyes, of the thoughts, of the purposes, of the devices, as well as of the feelings or affections of the heart. In Scriptural language, therefore, a 'new heart' does not mean simply a new state of feeling, but a radical change in the state of the whole soul or interior man.
It is plain that complete havoc must be made of the whole system of revealed truth, unless we consent to derive our philosophy from the Bible, instead of explaining the Bible by our philosophy.
Who would wish to see the reins of universal empire fall from the hands of infinite wisdom and love, to be seized by chance or fate? Who would not rather be governed by a Father than by a tornado? If God cannot effectually control the acts of free agents there can be no prophecy, no prayer, no thanksgiving, no promises, no security of salvation, no certainty whether in the end God or Satan is to be triumphant, whether heaven or hell is to be the consummation. Give us certainty-the secure conviction that a sparrow cannot fall, or a sinner move a finger, but as God permits and ordains. We must have either God or Satan to rule. And if God has a providence He must be able to render the free acts of his creatures certain; and therefore certainty must be consistent with liberty Charles Hodge, Systematic Theology II (301-302)
Original sin is the only rational solution of the undeniable fact of the deep, universal and early manifested sinfulness of men in all ages, of every class, and in every part of the world.
Many sincere believers are too introspective. They look too exclusively within, so that their hope is graduated by the degree of evidence of regeneration which they find in their own experience. This, except in rare cases, can never lead to the assurance of hope. We may examine our hearts with all the microscopic care prescribed by President Edwards in his work on The Religious Affections, and never be satisfied that we have eliminated every ground of misgiving and doubt. The grounds of assurance are not so much within, as without us. Systematic Theology (London, 1873), 3:107