In short, from the bible, from many pages of the bible. Now there is not a verse/sentence that commands these three means of establishing bible authority, but they are the only three that we can see the bible using or referencing time and again. While there is not a “one verse quote” that can be given to show these three things necessary, there is a portion of one chapter that is a good example of how God enabled man with the ability and necessity to understand His will through the means of direct commands, approved examples, and necessary inference.
Acts 15:6-21 demonstrates how the apostles (who were inspired by the Holy Spirit) and the first century church established God’s authority for their teaching and practice when sufficient revelation had already been made. In this chapter, a dispute among the brethren arose as to whether the gentiles were to be circumcised and follow the law of Moses in order to be saved. It is interesting that the apostles do not turn to the Holy Spirit for direct revelation on this matter; instead they rely on the revelation that had already been provided previously by the Spirit. So how did they go about determining the truth? Peter, in verses 6-11, makes his point on the basis of necessary inference. Notice the three facts that Peter makes use of to properly understand what God would have the Gentiles do: 1) Peter points out that earlier he was sent by God to preach to the Gentiles. 2) God acknowledged the gentiles by giving them the Holy Spirit even as He did to the apostles back in Acts chapter two. 3) God made no distinction between the Jews and the gentiles as to their salvation.
With these three facts laid out, Peter draws the necessary conclusion: “Now therefore, why do you test God by putting a yoke on the neck of the disciples which neither our fathers nor we were able to bear? But we believe that through the grace of the Lord Jesus Christ we shall be saved in the same manner as they” (10-11). Even though God did not specifically say that the Gentiles did not have to be circumcised or keep the law of Moses in order to be saved, Peter was able to necessarily infer that they were not under such a requirement because of the facts of how God went about saving Cornelius and his household.
Paul and Barnabas are next to speak in the chapter, and they take up after Peter using the idea of approved examples. An approved example is not something that we (mankind) have approved, but examples in the scriptures that God has approved as the right way of thinking or doing something. Paul and Barnabas begin by telling of their experiences in preaching among the Gentiles, and that God performed miracles through them as they preached the gospel to them. Their preaching did not speak of requirements of circumcision or anything else that can be found in the old law, and yet God showed his clear approval by through the miracles which they performed.
In verses 13-21, we see the use of direct commands (i.e. “book, chapter, and verse”) in scripture where God plainly approved the acceptance of the Gentiles. It is unusual for most people to reject the idea that direct commands are not important in establishing what has been authorized by God. It seems like the approved examples and necessary inference is where the struggle is. But have we ever taken a look at the laws of the land? Have we read through some of them? It is easy today to get our hands on that information through the internet. The laws of the land are listed and numbered, precept by precept (it’s definitely not an interesting read). A reading of the bible will show that God did not provide us with a book of just direct laws, one after the other, but rather He chose to establish his authority through other means as well, giving us examples to follow, and recording information and accounts that would leads us to one and the same conclusion by absolute necessity. These are the things that we saw in Acts 15, and the rest of the bible will consistently show the same things. Take a look for yourselves!