First, there is the testimony of one's own consciousness, or one's own spirit, as Paul puts it.
Second, there is the testimony of the Spirit of God—the Holy Ghost.
Third, there will be the results manifest to ourselves and to others; effects which testify just as reliably as the hanging fruit indicates the character and condition of any particular tree.
1. By the first class of evidence I do not mean a set of fanciful sensations, or frames of feeling, but such an exercise of our judgment, when we examine the facts before us, as will enable us to come to a sound and reasonable conclusion.
The witness of one's own spirit is largely a matter of consciousness and faith, and it works like this: 'I am not only conscious of God's revealed claims upon me, and my own duty to Him; but, as far as I understand, I have put myself in line with what He wants me to be and do. For instance, I am told that whilst God will sanctify me I am able to sanctify myself. I therefore ask, "Have I so far co-operated with Him as to come out and separate myself from evil?" If I am right I can say, "Yes, I have"; and as a further evidence of my sincerity I seek to abstain from all appearance of evil.'
I am also commanded to present myself for practical and joyful service, and I am told that I must believe such a sacrifice is acceptable because whatever touches the Divine altar is holy. Now, I can be quite sure as to my compliance with these demands, and my willingness to live as a sanctified soul ought to live. I know whether or not in these things I have done my part; and, if I know that I have, I can then reasonably trust God or reckon on Him to do His part. That is what Paul calls 'a good conscience toward God', and there is no presumption in such a conclusion.
If we turn to John's Epistle we shall see how plainly he puts the truth about assurance. 'If', says the Apostle, 'our heart condemn us, God is greater than our heart, and knoweth all things'; but 'if our heart condemn us not, then have we confidence toward God'. Without this conscious sincerity it is useless to pray for the blessing, for God cannot sanctify us whilst we are clinging to any known wrong or compounding with some doubtful habit or folly. If, on the other hand, we are conscious that we have no reserves, and accept by faith the cleansing Blood as the cure for our heart's plague, we may with all reasonableness say, 'I have the testimony of my own spirit'.
2. Let us look at the second class of evidence, namely, the testimony of the Spirit of God—the assurance of the Holy Ghost.
If we are to be quite certain about the important things in relation to the soul, we must have the expression of God's mind and approval. Nothing is made clearer in the Apostolic writings than the fact that it is our blessed privilege to have this Divine testimony. Paul not only tells us that 'the Spirit beareth witness with our spirit, that we are the children of God', but speaks of the marvellous manifestations of God in saved souls in subsequent revelations: 'We have received the Spirit, which is of God; that we might know the things that are freely given to us of God.'
On first thought we might say, perhaps, that the gift would speak for itself. But the Lord goes beyond that by giving us not only the blessing itself, but also the Spirit to assure us that we have got the blessing. John is on the same line when he says repeatedly about those spiritual blessings, 'we know', 'we know that we know', and the secret of sureness is made clear, 'we know by the Spirit which He hath given unto us'.