Update: Schisms and apostasy may have been caused during the first and second millennia AD by factors other than the professional practice of theology. I.e. schism and apostasy may have been largely caused by lack of genuineness about being a disciple of Christ.
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Theology does appear to be an esoteric science, having secret, for some people inaccessible knowledge on certain central topics, when one considers any of a number of facts.
Firstly there is the testimony from God's Holy Word.
(1) Christ Jesus is described repeatedly by different sources (Mt 13:10-15; Lk 8:9-10) as having taught deliberately in an esoteric way about the Kingdom of God.
(2) Christ Jesus also is described as having said that few people find the way to eternal fellowship with God (Mt 7:13-14).
(3) Christ also is reported to have said that only the obedient can and will receive the spirit of truth (John 14:15-17). This is echoed in Christ's warning that the way to life is difficult, through a narrow gate, suggesting obedience that is highly demanding (Mt 7:13-14).
(5) Saint Paul the Apostle described that the announcement of God's Kingdom and the rescue through Christ Jesus could not be perceived by people going into eternal condemnation, whose minds were blinded by "the god of this aeon", i.e. the Devil, the Satan (2 Cor 4:3-4).
(6) God is described also in the Old Testament as having a personal quality of following a principle of competition in communication, rather than cooperation, with certain types of people (Ps 18:26; Ps 25:12-14; Prov 1:7).
Secondly, the testimony of the Holy Bible is confirmed by what (perhaps) anyone can see in the experience of the universe.
(7) Simultaneous with the establishment of theology as a discipline of a university, i.e. as a universally accessible science, there was a catastrophic and since-then unretrieved loss of consensus among the community of nominal Christian theologians and practitioners on how a human being gains eternal fellowship with God (i.e. inherits the Kingdom of God). Although the first milennium also witnessed schisms (also thanks to the inability of theologians to preserve agreement), it is the second millennium of Christianity, when theology detaches from churches and runs its own course, that could be called the Age of Schisms.
This, despite the conditions for inheriting eternal life being the central topic of the New Testament's 27 books, whose study was already then circa 1000 years old.
As of A.D. 2017, the absence of consensus has persisted. For example, teaching on the topic of how to enter eternal life differs radically among the three main groups of churches, the Orthodox, the Catholic, and the Protestant.
(8) The academic/scientific interpretation of the New Testament is fractured and confused, lacking consensus on most or all of the texts that are focused on inheriting eternal life. The field of New Testament Studies can be compared with illegal genetics modification research, for its chaos and destructiveness. Only rarely does it produce beneficial (actual, relevant) knowledge (see for example the scholarship of Joachim Jeremias).
(9) Outward evidence of citizenship in the Kingdom of Heaven is found only among few. There are only few Christians who are martyrs, in the classical, original sense of losing earthly foundations (life, health, property, etc.) for the sake of their testimony and loyalty to their heavenly foundations. It is also very rare to observe the fruit of the Holy Spirit (cf. Galatians 5) among nominal Christians.
(10) Rationality requires obedience to God, given the incontrovertible evidence that a supreme God created the Universe and the infinite cost of being condemned to eternal Hell fire and torment (cf. Pascal's Wager). However, most people do not choose obedience.
(11) Rationality would also suggest that God, when making an eternal choice of who will live with Him and His family, will create severe tests of loyalty, where 'faking it' isn't possible. This would make it less plausible that eternal life could be inherited on the basis of making a certain confessional statement or doing certain actions (that could be performed mechanically).
Now, is there a way to prove objectively the existence of esoteric knowledge? Some pathways are worth considering:
(a) If the proper interpretation of the New Testament is hidden, then one would expect certain phenomena to be observable.
- No consensus on the interpretation of the New Testament.
- All attempts to formulate an objective description of how to inherit the Kingdom of God and eternal life will fail to gain agreement.
- Widespread claims by practising Christians that there is esoteric knowledge (cf. Christian mysticism) central to the practise of Christian discipleship.
(b) A technology whose operation is kept secret (hidden, esoteric) provides a simple example of being able to prove the existence of esoteric knowledge. The operation (work) of the technology can be seen; for example, a mobile phone is able to perform some operation. However, the way that the mobile phone does this is kept secret.
Generalising, the hypothesis that "how to do X is esoteric knowledge" fails to be refuted so long as it is possible to see X being performed, and yet no explanation (knowledge) of how to do X is forthcoming.
Returning to our case of the New Testament, and specifically its teaching on how to inherit the Kingdom of God (and eternal life), we see that if one can see that inheritance, and no explanation of how the inheritors have done so is forthcoming, then the knowledge of how to inherit can be said to be esoteric (hidden, secret).
Can one see inheritance of the Kingdom of God? One of the key texts that helps to answer this question is Romans 8:14-17.
14 For as many as are led by the Spirit of God, they are the sons of God. 15 For
ye have not received the spirit of bondage again to fear; but ye have
received the Spirit of adoption, whereby we cry, Abba, Father. 16 The Spirit itself beareth witness with our spirit, that we are the children of God: 17 and if children, then heirs; heirs of God, and joint-heirs with Christ; if so be that we suffer with him, that we may be also glorified together. (AKJV)
This text clarifies that one can see the preconditions of inheritance: (a) being led by the Spirit of God; (b) suffering with Christ; (c) glorification with Christ. It is difficult to believe that a person evidencing all these three preconditions would not inherit God's Kingdom and eternal life.
A very similar picture of the road to eternal life is found in Philippians 3:8-14.
8 Yea doubtless, and I count all things but
loss for the excellency of the knowledge of Christ Jesus my Lord: for
whom I have suffered the loss of all things, and do count them but dung, that I may win Christ, 9 and
be found in him, not having mine own righteousness, which is of the
law, but that which is through the faith of Christ, the righteousness
which is of God by faith: 10 that
I may know him, and the power of his resurrection, and the fellowship
of his sufferings, being made conformable unto his death; 11 if by any means I might attain unto the resurrection of the dead. 12 Not
as though I had already attained, either were already perfect: but I
follow after, if that I may apprehend that for which also I am
apprehended of Christ Jesus. 13 Brethren, I count not myself to have apprehended: but this one thing I do, forgetting those things which are behind, and reaching forth unto those things which are before, 14 I press toward the mark for the prize of the high calling of God in Christ Jesus. (AKJV)
Certainly, these texts from Saint Paul are consistent with the warning by Christ Jesus that the way to eternal life is hard-pressured and few find it. It is notable that both Pauline texts talk about the process of suffering with Christ and being glorified with Christ, in a way that is at least a little cloudy (mysterious? hidden? esoteric?).
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Notes
AKJV: KJV reproduced by permission of Cambridge University Press, the Crown’s patentee in the UK.