Memory of previous earth-lives can never arise within physical experience, unless the thoughts have, during those earth-lives, been directed to the spiritual world. It is always necessary first to have known of a thing in order that a clearly recognisable remembrance of it may arise later. Therefore we must, during one earth-life, gain knowledge of ourselves as spiritual beings if we are to be justified in expecting that in our next earthly existence we shall be able to remember a former one.
Yet this knowledge need not necessarily be gained through clairvoyance. When a person acquires a direct knowledge of the spiritual world through clairvoyance, there may arise in his soul, during the earth-lives following the one in which he gained that knowledge, a memory of the former one, in the same way in which the memory of a personal experience presents itself in physical existence. In the case, however, of one who penetrates into spiritual science with true comprehension, through without clairvoyance, the memory will occur in such a form that it may be compared with the remembrance in physical existence of an event of which he has only heard a description.