When God sent the incarnate Christ to exemplify himself and his Kingdom to mankind he chose to do so in the centre of a Mediterranean region mainly committed to the religion of Judaism.
Understandably, Christ’s short 3 year ministry was dominated by the need to correct Judaism’s misplaced expectation of their ‘birthright’ restoration to the earthly Jerusalem; punctuated only by brief asides such as “other sheep have I which are not of this fold, them also I must bring, and they shall hear my voice; and there shall be one fold and one shepherd”.
All of the writings canonised into an extension of Judaism’s ‘Old Testament’ were instigated by Jews with repeated reference to the #12 (tribes of Israel and appointed apostles, for example).
However, in “opening up Christ’s fold to his other sheep" the #12 mould was broken by the appointment of a 13th apostle in the person of Paul, whose writings taught that henceforth there would be “Neither Jew nor Gentile, for you are all one in Christ Jesus”.
Otherwise, the remaining New Testament writings (including Revelation in particular) where dominated by the repeated influence of the writers’ ingrained ‘#12’ religion of Judaism (and that applies to more than just Peter).
The burden of the ministry (mainly borne by Paul) is evident in his letter to the Galatians where he strives to counter the tendency of converted Jews to revert back to Judaism (“O foolish Galatians who hath bewitched you, I marvel that ye are so soon removed from him that called you into the grace of Christ unto another gospel").
I commend well established believers to read (again and again) the remainder of Paul’s letter to the Hebrews, beginning at chapter 6 verse 1-6
“Let us leave the elementary doctrine of Christ and go on to maturity. Not laying again a foundation of repentance from dead works, of faith toward God, of instruction about washings, the laying on of hands, the resurrection of the dead, and eternal judgment (which we will do if God permits).
For it is impossible to restore again to repentance, those who have once been enlightened, have tasted the heavenly gift, have shared in the Holy Spirit, have tasted the goodness of the word of God and the powers of the age to come, and then have fallen away, since they would thereby be crucifying once again the Son of God”
Paying particular attention to chapter 9 verses 7&8: “Into the second tabernacle went the high priest alone once every year, not without blood, which he offered for himself, and for the errors of the people: The Holy Ghost this signifying, that the way into the holiest of all was not yet made manifest, while as the first tabernacle was yet standing”