Things that are likely candidates for being primary in Christianity are things like a) the process of discernment – techniques and tools and skills to do this, b) cultivating a sense of grace in one’s life which then affects one’s daily actions and habitual states (which flows from a trusting relationship with God of a certain sort and an accurate understanding of one’s own abilities, i.e., humility of a certain kind), c) developing non-attachment to various stuff (and instead putting God in first place), d) incorporating central metaphors in Christianity such as God as Abba (Father) or us as descendents of a spiritual King (i.e., Princes or Princesses), and so on.
(This is not to say these Christian ideas are correct or more useful than certain other ideas. It is rather to say these sorts of things are what are primary to Christianity.)
Things that aren’t primary in Christianity are i) the exact nature of the Holy Trinity, and in particular what is the exact relationship of God the Son to God the Father, ii) how exactly God is an omni-God and what exactly this means, iii) the veracity of this or that verse from the Old Testament, and so on.
Many critiques of Christianity focus on what according to this pragmatic understanding of Christianity are theological minutiae or over-emphasize canonical scriptural elements. These critiques are essentially misled because Christianity isn’t primarily about these things. The critiques often stem from a misunderstanding within Christianity itself, which emphasizes the i) – iii) group’s sort of issues.
Also see here.