There is a person who is always worshipping God, and also never harms a soul. But he never helps others or explains what he knows. What could I call such a person?
I think sanctimonious may convey the idea:
affecting piety or making a display of holiness [C17: from Latin sanctimonia sanctity, from sanctus holy]
showing or marked by false piety or righteousness; hypocritically virtuous.
Also pharisaical :
- excessively or hypocritically pious; "a sickening sanctimonious smile"
P.S. Regarding "pharisaical" people should consider not using this term because of its anti-semitic connotations.
Based off your description the person:
- Worships a god (context may open or close certain answers, since different "gods" / religions will place emphasis on certain practices and not others).
- Does not negatively impact others.
- But also does not positively contribute to others learning or others well being.
I would lean toward describing them as either
- having or showing a dutiful spirit of reverence for God or an earnest wish to fulfill religious obligations.
- characterized by a hypocritical concern with virtue or religious devotion; sanctimonious.
Reasoning: This word captures the duty to deity, does not demand one be "good" (as in helpful), and yet leaves open the idea/connotation of hypocrisy if helping others is part of that religion.
feeling, exhibiting, or characterized by reverence; deeply respectful
Reasoning: The idea of respect is inherent in both the worship of the deity as well as in not hurting others. Yet respect does not imply that one helps.
hermit or eremite would fit.
hermit, also called Eremite, one who retires from society, primarily for religious reasons, and lives in solitude. In Christianity the word (from Greek erēmitēs, “living in the desert”) is used interchangeably with anchorite, although the two were originally distinguished on the basis of location: an anchorite selected a cell attached to a church or near a populous centre, while a hermit retired to the wilderness.
I think that self-righteous also conveys the correct meaning.
having or showing a strong belief that your own actions, opinions, etc., are right and other people's are wrong
convinced of one's own righteousness especially in contrast with the actions and beliefs of others : narrow-mindedly moralistic
You never know who will be offended by what, but I've never1 encountered the suggestion that any modern Jew might take offence at this dictionary.com definition...
pharisee 2. (lowercase) a sanctimonious, self-righteous, or hypocritical person.
The adjectival form is much less common, so you're more likely to hear "He's such a pharisee!" rather than "He's so pharisaical!".
Note that the original Collins definition (also cited by dictionary.com) differs slightly, in that it just says (often not capital). Which accords with my own experience; the "figurative" use isn't always marked by being in lowercase.
1 Until now (see comments below)
It probably depends on what religion the person ascribes to. I'll go with the assumption that the golden rule is a requirement in each religion. Following from that, it would seem that such a person is devout. They worship [Gg]od and treat others as they wish to be treated. If a religion does make it a requirement to actively engage others and help them, then such a person is sanctimonious.
Roughly half of the population are introverts though. There are great many self-help guides on how extroverts can deal with lack of human contact and how introverts can deal with excess of human contact.
If you are looking for a pejorative term to label such a person, just realize that you are taking the position that the introverted half of the population cannot be honest followers of such a religion. I am not saying that's right or wrong, but I am saying that it follows from a pejorative labeling of such a person.
I too would have gone for hermit or anchorite, but I feel it might be undesiredly too christian-oriented. Let's instead search for a term that does not imply a specific religion.
Solipsist alone covers well the detached from the world aspect but lacks to convey the religious fervor. So I'd advocate for :
A solipsist mystic
(as in a mystic has a deep and intimate relationship with his god, that is unsharable with others.)
So it could describe a buddhist as well as a christian, or any other faith.
(Note to the OP : I read in a comment that your question did not imply being retired of the world. Can you answer to that ? If so, I'll remove my answer for being off-topic.)