By Caspar David Friederich (1774-1840)
It is often said that mystical experience is ineffable, that is it cannot be expressed or comprehended... but this restriction applies to all possible communications.
Communication is, in the first place, always a partial, hence distorted or biased, summary of reality (because, in reality, everything is linked and there are an open-ended number of possible relevant factors) - and following that, the transmission and reception and comprehension of any communication is liable to limitations and errors.
So ineffability is a false and misleading definition. What is trying to be said is simply that the only truth about reality must be known directly, without any communication. Thus, all communication can do is point in the direction of truth - and to share a truth is for two or more persons directly to experience the same truth.
All true knowledge of reality is therefore a 'mysical' experience.
And any communication that claims to be true - whether it be in the form of mathematics, logic, science or anything else - is making a necessarily false claim.
I suspect that this is the general-language pointer at the truth which underpins the specifically mathematical/ logical assertion of Godel's incompleteness theorem. All Mathematics. Logic, Science is always incomplete - hence always wrong; and wrong in ways that that discipline can never know (because all disciplines are based on communications, hence are incomplete).
Direct or 'mystical' knowledge is therefore the only real knowledge; and each must know it for himself, from personal experience - else it is not known.