What does it mean the two become one?

There are thousands upon thousands who are united on earth to the real other self. Those so united will go on as one in the celestial world, but those so united do not remain apart very long—a natural law exists that when one departs from earth, the other soon follows—for those who belong together cannot be long separated—the half, which has departed draws the remaining half to itself, so that earthly husbands and wives who have been for long years separated by so-called death are not reunited and nearly all the widows and widowers left on earth soon marry again. This is as it should be, but those who thus marry were not in the first instance united to the eternal counterpart of themselves—if such had been the case they would not marry again—the very thought would be horrible to them. We do not mean to say that the husband or wife thus left may not have had a strong regard or one may call it love if one prefers, but the fact that they soon after united themselves to others is evidence in itself that they had not found the true one.

—Herr Franz in Spirit