I can imagine that the oceanic feeling could become connected with religion later on. That feeling of oneness with the universe which is its ideational content sounds very like a first attempt at the consolations of religion, like another way taken by the ego of denying the dangers it sees threatening it in the external world.

In my Future of an Illusion I was concerned [...] with what the ordinary man understands by his religion, that system of doctrines and pledges that on the one hand explains the riddle of this world to him with an enviable completeness, and on the other assures him that a solicitous Providence is watching over him and will make up to him in a future existence for any shortcomings in this life. The ordinary man cannot imagine this Providence in any other from but that of a greatly exalted father, for only such a one could understand the needs of the sons of men, or be softened by their prayers and placated by the signs of their remorse. The whole thing is so patently infantile, so incongruous with reality, that to one whose attitude to humanity is friendly it is painful to think that the great majority of mortals will never be able to rise above this view of life.