Thus far we've seen that OT Israel and the disciples of Jesus both found themselves confronted by solid, fleshed-out revelation, and that they were bound to confine themselves to that revelation, whether it was the Sinai covenant as the provisional revelation of God or Christ himself as the final revelation. But what about the post-ascension world in which we live? Well, the NT gives us the answer in a number of ways and in a number of places.
We could start off still in that last discourse recorded in John's gospel. A lot of the groundwork for the post-ascension church is laid here. Note particularly 15:26-27, and 16:12-15. These passages describe the work of the Holy Spirit in revelation. Given their position in the discourse, and some of the things that are said in chapter 15 ("you have been with me from the beginning") we should see these verses as applying to the apostles and not to all Christians, as attractive as that might be. Jesus is promising here that the Holy Spirit will both remind the apostles of what Jesus has said to them, and will guide them into truth that he has not been able to explain to them. The apostles, along with the Holy Spirit, are to bear witness to Christ.
A similar point could be made from the great commission in Matthew 28. The apostles are sent by the authoritative Lord Jesus to make disciples, "teaching them to observe all that I have commanded you". It is in this capacity that they receive the promise of Christ's perpetual presence ("to the end of the age"), and I am quite tempted to go along with Barth in attaching the promise to their witness rather than their persons. But that may be pushing things.
We get to see how this works out in Acts and the Epistles. Just a few brief instances to highlight. Firstly, I have always thought it significant that when Paul says farewell to the elders of the church in Ephesus, he commends them "to God and to the word of his grace" - not to any replacement human minister. This is interesting not least because Timothy will have a lengthy period of ministry in Ephesus later. The point is that the message the apostles preached is to be the thing that guards the churches, not human successors to the apostles.
In this connection, it is also worth considering Paul's outburst in Galatians 1:6-9 against any preaching of a gospel contrary to that which he preached. He self-consciously stands on his authority as an apostle, commissioned by Christ to bear witness, but also allows for the (albeit hypothetical) possibility that he himself could go wrong and preach another gospel himself, in which case he should be ignored. The pastoral epistles generally make similar points: what Paul's successors are to do is pass on what they heard from him (e.g. 2 Tim 2:2), and to maintain the apostolic deposit without alteration.
Ponder also the introduction to 1 John, with its emphasis on the apostles right and qualification to be witnesses, uniquely commissioned. Note that fellowship with God is only possible through fellowship with the apostles (1:3)! And consider 2:18-27 - antichrist is defined as one who denies the apostles' witness to Christ, and thus leaves their company; antichrist is to be combatted by abiding in the truth they have already heard in the power of the Spirit.
All in all, the NT church finds itself confronted by solid, explicit revelation in the form of the apostles' witness to Christ. Again, we have a situation where it is not permissible to look anywhere else for knowledge about God. This apostolic deposit cannot be ignored, cannot be refined, cannot be slimmed down, cannot be got behind - not if we want to know God.
Tomorrow: probably the conclusion...