CH Mackintosh on Assurance

This is from Part 3 of The Christian: His Position and His Work. I am going to be putting the whole book, along with other works from C.H. Mackintosh on the church library page here.

"It is absolutely essential to the enjoyment of settled peace that the heart should rest solely on the authority of holy scripture. Nothing else will stand. Inward evidences, spiritual experiences, comfortable frames, happy feelings, are all very good, very valuable, and very desirable; indeed we cannot prize them too highly in their right place. But, most assuredly, their right place is not at the foundation of the Christian position. If we look to such things as the ground of our peace, we shall very soon become clouded, uncertain, and miserable.
The reader cannot be too simple in his apprehension of this point. He must rest like a little child upon the testimony of the Holy Ghost in the word. It is blessedly true that "He that believeth hath the witness in himself" And again, "The Spirit itself beareth witness with our spirit that we are the children of God." All this is essential to Christianity; but it must, in no wise, be confounded with the witness of the Holy Ghost, as given to us in holy scripture. The Spirit of God never leads any one to build upon His work as the ground of peace, but only upon the finished work of Christ, and the unchangeable word of God; and we may rest assured that the more simply we rest on these the more settled our peace will be, and the clearer our evidences, the brighter our frames, the happier our feelings, the richer our experiences.
In short, the more we look away from self and all its belongings, and rest in Christ, on the clear authority of scripture, the more spiritually minded we shall be; and the inspired apostle tells us that "to be spiritually minded (or, the minding of the Spirit) is life and peace." The best evidence of a spiritual mind is child-like repose in Christ and His word. The clearest proof of an unspiritual mind is self-occupation. It is a poor affair to be trafficking in our evidences, or our anything. It looks like piety, but it leads away from Christ — away from scripture — away from God; and this is not piety or faith, or Christianity.
We are intensely anxious that the reader should seize, with great distinctness, the importance of committing his whole moral being to the divine authority of the word of God. It will never fail him. All else may go, but "the word of our God shall stand for ever." Heart and flesh may fail. Internal evidences may become clouded; frames, feelings, and experiences may all prove unsatisfactory; but the word of the Lord, the testimony of the Holy Ghost, the clear voice of holy scripture, must ever remain unshaken. "And this is the word which by the gospel is preached unto us."