The New Testament is, in its essence, an invitation to share fellowship with God and with the apostles. This is stated very clearly at the opening of the First Epistle of John, that is 1 John, chapter 1, verses 1 through 4.
"That which was from the beginning, which we have heard, which we have seen with our eyes, which we have looked upon, and our hands have handled concerning the Word of Life‑ [and John is speaking there about the Word made flesh, that's Jesus, and he goes on in verse 2:] the life was manifested, and we have seen, and bear witness, and declare to you that eternal life which was with the Father and was manifested to us‑ [understand he's speaking about Jesus. Then he goes on:] that which we have seen and heard we declare to you, that you also may have fellowship with us; and truly our fellowship is with the Father and with His Son Jesus Christ." (NKJ)
John is writing as one of the apostles who have brought to us, in the New Testament, their own personal witness and record of what they saw and experienced with Jesus. And then he adds the reason why this New Testament record has been transmitted to us by the apostles. The ultimate purpose, there in verse 3 ‑ "that you also may have fellowship with us [that's the apostles] and truly our fellowship is with the Father and with His Son, Jesus Christ." So, in that way, the New Testament is an invitation to all who read it to share fellowship with the apostles, and the fellowship that they have is with the Father and with the Son, Jesus Christ.
So we can put it this way: the New Testament is an invitation from God, through the hand of the apostles, to come into and enjoy the fellowship that God the Father and God the Son have together eternally. It's an invitation to enter into and enjoy the eternal fellowship of the Father and the Son. That's the end purpose why the New Testament was written and if we don't enter into that, then we've missed the purpose for which the New Testament was given to us.
In that connection, John adds one more purpose for his writing. In verse 4:
"These things we write to you that your joy may be full." (NKJ)
So, the result of entering into this fellowship is fullness of joy and if we stop short of the fellowship, then we do not have the fullness of joy that God wants us to have and that He's made available to us through the New Testament. So understand this: the end purpose is fellowship with God.
Father, thank You that You have invited me into the fellowship with you, and your Son Jesus, through the Holy Spirit., that my joy may be full. Please help me to fully accept that wonderful invitation. In Jesus Name, Amen!