Q: I have just been initiated into japa meditation. I just wondered: is the mantra a sound or a word?
And if Atman and Brahman are one, I am interpreting that correctly to mean that in my deepest Self (soul) I am divine – at one with Brahman? And that that signifies a unity (oneness) not sameness (identity)?
To put it in Christian terms, in my soul the Spirit of God dwells (as Eckhart said: ‘the I with which I see God is the same I with which God sees me’ and ‘my ground is God’s ground, God’s ground is my ground’).
Thus Advaita: ‘not two’ (but not completely one either – monism). In Christianity: ‘whatever you do to the least of these, you do unto me’ (Matthew 5: 45).
A: ‘japa’ meditation is the mental repetition of a sound or a mantra. You could use the name of a god but it would still function as a sound. I.e. you are not supposed to ‘think’ about it, dwell on its significance etc. – that is a different form of meditation entirely. You give attention only to the repeating sound, ignoring any other thought. The repetition gradually loses its intensity and frequency and you are eventually left with complete mental silence. (May take a few years to get to this point!)
Atman and Brahman are two words for the same non-dual reality. The former is from the perspective of the (apparent) person and the latter from the as-if-perspective of absolute reality. Ishvara is the name given to Brahman from the perspective of empirical reality. Everything (including you and Ishvara) is simply name and form of Brahman. The relevant metaphor is that of bangle, ring and necklace being name and form of gold.
It would be best for you to temporarily forget all about Christianity and any other religion/philosophy until such time as you fully understand Advaita. Then you will be able to see that all the others are attempts, with varying degrees of success, to approach an understanding of the same truth. Trying to reconcile the views will only lead to confusion.