Again, on the other side, great devotees like Manikka-vasagar, Nammazhvar, Arunagiri-nathar, Tayumanavar, etc. have themselves been convinced advaitins, and this is reflected in innumerable flashes in their compositions.
If a jnAni should not do a Bhakti composition, then I would say that he should not also do a work of jnAna. Why am I saying this? Let us go back to the definition of a jnAni. The world is all mAyA; the thinking of people as if they were separate separate jIvAtmAs is nothing but Ignorance - with such a conviction through personal experience, they have thrown away that Ignorance as well as its basic locus, the mind, and they live in the non-dualistic state of "I am everything" - such should be the status of the jnAni; shouldn't it be so?
Such a person preaching, or writing a book, even if it be about the subject of jnAna - is it not a contradiction? Unless such a person thinks there is a world outside of him and there are jIvAtmAs outside, how can he think of teaching? Teaching whom?
And when we look at it this way, all those great teachers of jnAna should really not be jnAnis ! What power will there be for such a teaching about jnAna from teachers who are not jnAnis themselves?