[CS Lewis’s and Richard] Baxter’s “mere Christianity” was not “mere” Christianity in the weak, attenuated sense of the word mere.
Both Lewis and Baxter used the word mere in
what is today—regrettably—an obsolete sense, meaning “nothing less
than,” “absolute,” “sure,” “unqualified,” as opposed to today’s weakened
sense of “only this,” “nothing more than,” or “such and no more.”
contemporary meaning of the word mere corresponds to the Latin vix, “barely,” “hardly,” “scarcely,” while the classical, Baxterian usage corresponds to the Latin vere, “truly,” “really,” “indeed.”
Baxter had no use for a substance-less, colorless homogeneity bought at
the expense of the true catholic faith. Indeed, he had his own list of
non-negotiable fundamentals, including belief in one triune God; in one
mediator between God and man, Jesus Christ, the eternal Word, God
incarnate; in the Holy Spirit; in the gifts of God present to his
covenanted people in baptism and Holy Communion; and in a life of
obedience, holiness, and growth in Christ.
It is surely correct to focus on what is “truly,” “really,” “indeed" - but the list of 'non-negotiable fundamentals' has come to look more and more misguided; as the denominations which officially hold to these fundamentals have become less and less 'mere' in the sense of truly/ really/ indeed - but have assimilated almost invisibly into the prevalent Western secular Leftism.
'One triune God' is hardly a useful discrimination - except to distinguish Christianity from pure monotheism minus Christ - since it amounts to espousal of a paradoxical or non-common-sensical form of words. It is, indeed, a ludicrous misrepresentation to put 'one triune God' first and foremost as a 'mere' Christian belief - when this is not even stated in the Bible (only in creeds from many generations later), but extracted from an elaborate close reading of the text combined with philosophy at a high level of abstraction!
Clearly Mere Christianity entails acknowledging Christ as our Lord and Saviour - but there are counter examples to the need for baptism and Holy Communion in some low church Protestant groups that certainly seem Christian - such as the Salvation Army.
And while a life of obedience, holiness and growth in Christ are certainly desirable and pleasing to God; the essence of the Gospel is that none of these are necessary for Salvation - thank Heavens, or else hardly anyone would ever be saved!
A better definition of real Christianity would therefore need to be much simpler and less parochial on the one hand - to include more than the mainstream 'catholic' churches (Orthodox, Roman, Anglican) ; while on the other hand much more rigorous in excluding the mass of clergy and laity in these 'catholic' churches who are happy to repeat 'orthodox' forms of words in creeds and catechisms - but who in practice systematically (and indeed aggressively) subordinate Christianity to the changing expediencies of secular politics.