Waite a Christian, I dunno without offending anyone, is like saying an active IRA member is Catholic, or a terrorist is a Muslim..
That's a bit OTT I think in relation to Waite - though it would be a closer analogy to the 'Roman Catholicism' of Levi though perhaps!
I don't know exactly how to justify Waite's claim that he was a Christian.
A useful summary of Waite's faith is in the very short
Afterword on
'The Faith of A. E. Waite' in
'A. E. Waite - A Magicain of Many Parts' by R. A. Gilbert.
I suppose, at a stretch and for the sake of argument, that to an extent it might be said that he
Re-Christianized the tarot, by his rejection of some of the Egyptianization of the Tarot of former Tarot esotericists that concealed or ignored and on occasion blatantly twisted its original Christian content.
How was Waite actually Christian?
While he acknowledged 'there have been many saviours' he believed 'Christ was the last and the first'. He was sacramentalist (his book on the Holy Grail is at root about the Christian mysteries of the Sacrament of the Eucharist). He believed in Atonement (albeit like Levi his belief was unorthodox, believing in the Origen 'heresy' of Universal Atonement).
As far as I know he didn't follow any particular denonimation, didn't eat fish on Fridays or go to Church on Sundays- but thereagain of many people who do, there are to be found many who I would count as far less 'Christian' than A.E. Waite!
On the Hermeticism of the Christian Mystic - what such may believe and practice, here is an interesting little essay on Evelyn Underhill, who was a member of Waite's off-shoot of the Golden Dawn:
http://www.evelynunderhill.org/articles/2003_spiritualtransformation.pdf
(that they all were teaching the same thing - the marriage of the Hierophant and the Shekinah (Priestess) in one's heart that gives birth to God within).,
This is a theme he explores in several of his works (The Secret Tradition in Israel for example), along with that of the pilgrims journey (in tarot for example, the Fool's as Prince in exile traveling through this world - a theme later to inspire Eden Gray's concept of "the Fool's journey' in tarot) and alchemy. Common themes of Hermetic Christian Mysticism:
"In Mysticism, Underhill distinguishes three narratives
by which Christian mystics have traditionally
tended to express their spiritual journeys.
These are: i) the craving for home -- the narrative
of the pilgrim or wanderer; ii) the craving for
one’s beloved -- the narrative of the spiritual marriage;
and iii) the craving for regeneration, transmutation,
purity, and perfection -- the narrative of
the Christian Hermeticist or spiritual Alchemist."