This commandment is given to those who want to be disciples of Jesus. So obviously once if some one says I believe in Jesus his next commandment given by Jesus is to love the neighbour. So I have written from the context of a believer.
I think that one of the things that is overlooked about this passage is its Trinitarian nature. Faith is the Holy Spirit, Hope is Christ, and Love is of course God. Hence the great truth in that the greatest of these things is Love.