According to Allan Kardec, the different feelings we experience around friends versus enemies is due to a physical law of vibrational assimilation and repulsion. Evil thoughts create unpleasant vibrations while good thoughts create agreeable vibrations, influencing our sensations of others approaching. Loving one's enemies represents a sublime application of charity and a victory over selfishness and pride.

1. The diversity of feelings in these two very
different circumstances is the result of a
physical law, which is the assimilation and
repulsion of vibrations. An evil thought
produces a vibrationary current which
causes an unpleasant impression. A good
thought encompasses us with a very
agreeable emanation. This is the reason for
the different sensations which are
experienced on the approximation of a
friend or an enemy. (Allan kardec)

2. If the principle of charity is to love one neighbours, then to
love one enemies is the most sublime application of this same
principle, seeing that the possession of this virtue represents
one of the greatest victories which can be achieved against
selfishness and pride.
Allan kardec

3. The diversity of feelings in these two
very different circumstances is the
result of a physical law, which is the
assimilation and repulsion of
vibrations. An evil thought produces a
vibrationary current which causes an
unpleasant impression. A good thought
encompasses us with a very agreeable
emanation. This is the reason for the
different sensations which are
experienced on the approximation of a
friend or an enemy. Allan kardec