25 “These things I have spoken to you while I am still with you. 26 But the Helper, the Holy Spirit, whom the Father will send in my name, he will teach you all things and bring to your remembrance all that I have said to you. 27 Peace I leave with you; my peace I give to you. Not as the world gives do I give to you. Let not your hearts be troubled, neither let them be afraid. 28 You heard me say to you, ‘I am going away, and I will come to you.’ If you loved me, you would have rejoiced, because I am going to the Father, for the Father is greater than I. 29 And now I have told you before it takes place, so that when it does take place you may believe. 30 I will no longer talk much with you, for the ruler of this world is coming. He has no claim on me, 31 but I do as the Father has commanded me, so that the world may know that I love the Father. Rise, let us go from here. (John 14: 25-31)
Jesus promises the Helper, the Holy Spirit. The task before the apostles is great and it is something they will not be able to do themselves. The Helper will come and bring to remembrance all that Jesus has taught them. The disciples need this because they are to make disciples by baptizing them in the name of the Father and of the Son and of the Holy Spirit and teaching them everything he has commanded them. That would be a daunting task, to remember everything Jesus taught them during his three year earthly ministry. But the Holy Spirit would continue Jesus work by teaching them all things and reminding them of everything Jesus had said.
This is why we believe that what the apostles have written is inspired. They were given the Holy Spirit in a manner that the Holy Spirit hasn’t been given to us. Not that we don’t have the Holy Spirit, but the Holy Spirit had a different task with the disciples. It is through the disciples then, that the Holy Spirit teaches us all things. That is everything that we need to know. The apostles themselves were not taught everything, they never were given the date of Christ’s return for instance. Instead they are given what they need to know as disciples of Christ, and left with peace that comes from knowing that in Jesus we are reconciled to the Father and made right. And to accomplish that the rise and leave.