There are many riches of spirit to be found in Aikido for those willing to seek them, whether Christian or otherwise. I will suggest a few things and sources here to further your interest
The words of the founder regarding Christianity are appropriate here, given your initial post. André Nocquet studied with Morihei Ueshiba, the founder of Aikido, in1955 as uchi-deshi ("live-in student"). Noquet later became president of the European Aikido Federation. He recounts this in Aiki News #85 (Summer 1990):
Ueshiba Sensei had a great deal of respect for Christ. I was living in a four-mat room in the dojo and he would knock on the door and enter. He would sit down beside me and there was a portrait of Jesus Christ. He would place his hands together in a gesture of respect. I asked him one day if there wasn't a similarity between his prophecies and those of Christ. He answered, "Yes, because Jesus said his technique was love and I, Morihei, also say that my technique is love. Jesus created a religion, but I didn't. Aikido is an art rather than a religion. But if you practice my Aikido a great deal you will be a better Christian.
Kotodama is perhaps the most arcane, and least understood element of O-Sensei's spiritual practice related to Aikido, especialyl for Westerners since it is intricately interwoven into the structure of Japanese as a language system. Kotodama is a native Shinto system of devotional or spiritual practice attributing metaphysical action to word-sounds (kotodama="word-spirit") I agree that Sensei Gleason's book is perhaps the best attempt to lay out these ideas for the Western reader. Peter Goldsbury's article "Touching the Absolute" cited bleow is also helpful.
Kotodama has both analogous (similar in form) as well as homologous (similar in origin) connection to the pagan and Christian idea of Logos, through Shingon ("True Word") Buddhism and the Silk Road, as O-Sensei himself acknowledged in "Takemusu-Aiki: Aikido-Kaiso-Ueshiba-Morihei-Sensei-Kojutsu," Hideo Takahashi, ed., 1976, p. 86; attributed and translated by Peter Goldsbury, "Touching the Absolute: Aikido vs. Religion and Philosophy" Aiki Journal, http://www.aikidojournal.com/article.php?articleID=2
Takemusu Aiki wrote:
""Kirisuto ga ‘hajme ni kotoba ariki' to itta sono kotodama ga SU de arimasu. Sore ga kotodama no hajimari de aru." (‘In the beginning was the Word', spoken by Christ is this kotodama SU. This is the origin of kotodama.)"
Lastly, you should consider the significance of O-Sensei's Doka "Songs of the Way" that illustrate in poetical or epigraphic form important principles about aikido and it pracitce and applciation ot larger concerns. A convenient source for the pre-war and post-war doka can be found here: http://www.aikidofaq.com/doka.html
Notable for the devout Christian, especially in light of the connections between the practice of kotodama and the idea of Logos are these Doka (with romaji and English translation according to John Stevens "The Essence of Aikido"):
John Stevens -The Essence of Aikido wrote:
kami no shikumi no
kami no samuhara
Brave and intrepid,
the cross of harmony (love)
is an instrument of kami
Utilize the Eight Great Powers
the Divine Plan [for regeneration]
nushi no tsukurishi
this form of
heaven and earth --
all created by the Lord,
we are members of one family.
(Stevens notes that the kanji read as "Lord" is also the root kotodama "SU")
John Stevens -The Essence of Aikido wrote:
Su no mioya
shiai no kokoro
yo no itonami no
moto no narinuru
SU, Exalted Father
with a heart of love
as vast as the sky--
it is the source of all that
functions in this world.
The Aikido FAQ version ( which is the translation of Abe Sensei) has this:
The spiritual essence of the Heavens and Earth
Congealing becomes the Way of the Cross-Shape +
Harmony and Joy make up the Floating Bridge
That binds this world together.
I will leave you to ponder the significance of this in light of traditional Christian theology.
Lastly, I leave you with these doka from the two sources I have given, which despite my ecumenical gloss, is the true heart of O-Sensei's teaching, and the only thing you really need to know to embrace the spiritual richness of aikido:
The Essence of Aikido wrote:
hiji mo keiko mo
mae zo mietari.
Progress comes to
those who train in the
inner and outer factors.
Do not chase after "secret techniques,"
for everything is right before your eyes!
AikidoFAQ: Doka wrote:
In these teachings listen most
To the rhythm of the strike and thrust
To train in the basics (omote)
Is to practice the very secrets of the art.