One devotee may want Krishna as his supreme master, another as his personal friend, another as his son and still another as his lover.
Krishna helps the devotees by giving them rememberance and knowledge so they can worship and serve Him–because that is what the devotees want, they want to remember Krishna, so Krishna helps them. They want to become the supreme lord themselves, they want others to serve them, they want to be the master–they do not want to surrender to Krishna, they do not want to even know that there is a Supreme Personality of Godhead above them.
So for a devotee Krishna appears as Krishna in a relationship like son, friend of lover and for the demon Krishna appears as the demon can believe that Krishna does not exist.
Therefore Krishna is revealing Himself to everyone in the way they want to see Him or if someone does not want to see Him Krishna is hiding Himself from them. Madhudvisa dasa Madhudvisa dasa My first contact with a Hare Krishna was a most merciful Mataji in Oxford Street, London who sold me a "Higher Taste" cook book in 1984 while I was on holidays there.
The thing that can not be changed, the eternal characteristic of that object. So if we are to love Krishna in a voluntary way then there has to be some other option for the rebellious living entities who decide not to love Krishna.
That is this material world and because Krishna reciprocates with all the living entities in the way they want to see Him then it is His great mercy for the demons who have rebelled against Him the He creates this material world as a place where the demons can forget Krishna and try to be happy separately from serving Krishna.