For you did not receive a spirit that makes you a slave again to fear, but you received the Spirit of sonship. And by him we cry, “Abba, Father.” The Spirit himself testifies with our spirit that we are God’s children. Now if we are children, then we are heirs – heirs of God and co-heirs with Christ, if indeed we share in his sufferings in order that we may also share in his glory. (Romans 8:15-17)

Jesus Christ attained for his chosen ones more than acquittal, as precious and necessary as that is, but in his exceeding kindness, God adopts them as his children and transforms them into the likeness of his Son. Then, his Holy Spirit causes them to be confident in his enduring love toward them, and to be confident in their place as his children. Therefore, a certainty that one has been rescued from condemnation does not go far enough. God has made us his very children, and he wants us to know it.

It is not a question of “Am I a member of this club?” That is a wrong way to regard the issue. When God converts a man through faith in Christ, the Spirit of sonship or adoption enables and inspires the person to address God as “Father.” This is at the same time an indication of who God is to the man and who the man is to God. It becomes natural for the man to call God his Father because the man is a child of God. In other words, the confidence of adoption is not contingent on something that you have but concurrent with something that you are. This confidence is not an implication derived from something that we do or have done, but it is an identification with what God has made us. You are one who calls God your Father.

Paul writes, “The Spirit himself testifies with our spirit that we are God’s children.” Thus the knowledge of our salvation is not a piece of information that we discover, but it is information that the Spirit of God testifies to independent of our effort or our subjective state of mind. Whether the emphasis is on the Spirit testifying to our spirit or along with our spirit, it is information that is announced, even imposed on us, by a foreign person and power.

God has made us into his children, so that we call him Father because of what we are, and the Spirit of God testifies to and with our spirit that we are his children. The result is not a subjective mindset or attitude, but knowledge and certainty. You are what you are – a child of God. And the Spirit says what he says – you cannot make him do it and you cannot stop him from doing it. When God testifies to something to and with your inner being, and when he has made you into that very thing that he testifies about, there is unavoidable knowledge. There can hardly be a more certain form of knowledge even in the life to come.

There is a distinction between the private aspect and the public aspect of our relationship with God, and where the issue of knowledge applies, there is a distinction between private knowledge and public knowledge. Unless we possess omniscience, or almost omniscience, so that we know all the thoughts of all the believers in all of history as they commune with God in their minds, then this distinction is evident and undeniable. And this distinction will persist in the life to come unless we will gain omniscience, or almost omniscience, to know all the thoughts that the saints shall place on the altar of their minds in all of eternity. The distinction between private and public stands even if only one person has only one private thought before God in all of history. This is so not only because we lack omniscience, but because God sees to it that this is the case: “I will also give him a white stone with a new name written on it, known only to him who receives it” (Revelation 2:17). This private aspect of our relationship is precious to him, and he will not relinquish it to avoid upsetting our theological traditions and philosophical theories.

This distinction is usually not mentioned when we summarize the Christian faith as an intellectual system and when we engage non-Christians in debate. The reason is that in these contexts the aim is to present the biblical worldview as a public philosophy. The Bible is a public revelation of the history and worldview of the Christian faith. The information is accessible to all to be studied and discussed. This public revelation is what we declare to believers and unbelievers, and it is what we defend before its detractors. The Spirit’s testimony that I am a child of God is not what I preach. And it is the Christian faith as a worldview and not myself as a believer that I defend when I face the critics.

Both our private knowledge and our public knowledge in the life to come rest on the same basis as the public knowledge that we now possess – all knowledge comes from God’s mind and becomes ours by his action. In the study of philosophy and apologetics, we establish that there is no knowledge apart from what we derive from the Bible. The context is the kind of public knowledge available to us in this life. In effect, this means that our public knowledge in this life is limited to what God has revealed in the Bible, and our private knowledge is limited to what God would cause us to know as stated in the Bible, including the knowledge of adoption. Thus this distinction between private and public knowledge does not leave room for the non-Christian to derive even private knowledge, since their sensations and speculations remain unreliable. And the Christian’s private knowledge of his place in Christ is not derived from his sensations and speculations, but it is caused by an action of the Holy Spirit that the man can neither initiate nor prevent.

To further illustrate, consider the innate knowledge of God mentioned in Romans 1 and 2. There it is said that all men possess knowledge of the nature and the power of God as well as the moral requirements of the law apart from the public revelation of Scripture. Although all men possess this knowledge, it is private in the sense that it is internal, so that it is not subject to public examination and cannot be the basis for public declaration – one man cannot examine another man’s innate knowledge of God, even if both of them possess it. (Indeed, the influence of this private knowledge is often evident in men’s public philosophy, but the knowledge itself remains internal.) This has some similarities to the private knowledge that the chosen ones receive regarding their place in Christ, but there are important differences. The confidence of sonship is not possessed by all men, but only by Christians. And they have this knowledge not because of their natural constitution as those made in the image of God, but because of the special operation of the Holy Spirit.

Christian doctrine must affirm that a private confidence of sonship is possible, and that it is a reality for the believer. It must affirm its possibility because the public revelation of the Bible makes room for it, and it must affirm its reality because the public revelation of the Bible declares it as an operation of the Holy Spirit in the Christian. Although some oppose this doctrine, the Spirit still testifies to my spirit, apart from my effort, that I am a child of God. It is an objective divine work, and not a subjective belief or attitude. It is not a matter of self-discovery. If he does not testify the same about you, how is that my fault? But some wish to divert attention from their own lack of certainty, and some would crucify the Bible to protect their own tradition or philosophy.

The testimony of the Spirit is a secret operation that results in private knowledge. The Spirit testifies to my spirit that I am a child of God. Again, this is usually not mentioned because we do not relate to one another on the basis of the Spirit’s internal testimony. The Spirit does not tell you what I am. You will have to judge me according to the public revelation of the word of God. You must interact with me and examine my confession, my character, and so on. I cannot preach the Spirit’s testimony to the non-Christian, and it would offer him little personal profit to believe that I am a child of God. Rather, I must declare to him the gospel and the doctrines of Jesus Christ, so that he might believe and become a child of God.

Now if we are children of God, then we are also heirs of God, even co-heirs with Christ. Because of this, we have the confidence to endure suffering, knowing that if we share in his sufferings, we shall also share in his glory. On the other hand, non-Christians lack the Spirit of adoption and his testimony that they are children of God. They shall inherit nothing but fire and brimstone.