We look upon kissing as a thoroughly normal expression of the libido, although it is true that the erotogenic zone in this case serves the purpose of object-love. The kiss does not claim the significance of a final sexual aim, but only represents a preparatory act.
Abraham positions the kiss as the canonical evidence that the oral erotogenic zone persists into adult libidinal life, functioning as preparatory rather than terminal sexual activity, while acknowledging that for some subjects it may become the essential aim itself.
, Selected Papers on Psychoanalysis, 1927thesis