a reincarnation, or are new souls or entities also introduced from time to time? And if so, how would we know the difference?
Most schools of Hinduism would argue, I think, that everyone has previous lives (not all of which were on this earth, or this physical realm, however). I think Hasidic Judaism may posit that some souls have been (relatively) recently created, though.
In Islam and Christianity there is no rebirth for the soul. The soul gets human birth only once. After this human birth the soul will either go to the Lord or will go to the hell permanently. Only one Lord created this entire universe. Therefore the policy should be the same for all the souls in this universe. There is only one Lord. All the souls are equal to Him. Can you deny this? If you don’t agree with this theory, you can follow your own faith. But your faith is not important. The truth is important. What ever is true, that alone happens and not as per your faith. If you agree with this policy I can correlate all the religions.
If you can correlate all the religions in a better way, I will also agree with you. If you are not caring for the correlation and follow your faith only, there is nothing for me to preach you. My correlation of all the religions is like this : In Gita two paths are explained. In the first path one goes to Brahmaloka without returning back. In the other path one returns back to this earth and falls in the cycle of births and deaths which is the wheel of Samsara. In all the religions there are only two paths. Reaching Brahmaloka is reaching the Lord. Falling in the cycle animals and births is going to the hell permanently. The soul which, has fallen in this hell will never get the human rebirth in which there is facility of trying to reach Brahmaloka. Not getting such a spiritual human rebirth is the absence of rebirth.
The soul which, goes to Brahmaloka will never get the rebirth of animals and birds and in such sense this soul also has no rebirth. But one point is to be understood carefully. The birth of animal, bird, worm etc., does not mean the actual animal or bird or worm etc., There are several human beings who live like animals, birds and worms. Such human births are also the births of animals, birds, worms etc., We are seeing such human beings in majority on this earth. They are immersed in the worldly bonds like money, children etc., They cannot cut their blind love to these worldly bonds. Even if they put some spiritual effort, it is incomplete because of the attachment with these bonds.
Such souls when they go to the upper worlds are also involved in such bonds in the upper worlds also. They can never attain Brahmaloka by preaching any amount of divine knowledge to them. But if they are not preached they will blame the Lord during the enquiry posing that they might have attained Brahmaloka, had they received the divine knowledge. The Lord preaches them also only to save himself from such blame and not to save them. Therefore if you are having all the facilities and also interest in the spiritual line this is the best birth for you and this is the only chance for you. If you waste this human birth you are falling into the births of animals etc., You are not given such chance again.
Islam and Christianity say that the soul has to wait for the final enquiry which, is to be done at the end of this world. This human body (Pindanda) is stated as the world (Brahmanda). The human body is a mini world containing the same components. Therefore the death of this human body can be treated as the end of this world from the point of the soul. You can also treat the day as birth and night as death. Veda says that the deep sleep is equal to death (Naviduhu Sati Sampatsyama Iti). Gita also says the same (Prabhavantyaharagame). Therefore the feelings (Samskaras) of previous births mean only the feelings of yesterday.
If you are on the spiritual line and if you are making sincere spiritual effort to cut these worldly bonds and to strengthen the bond with the Lord, your lifetime can be extended by the Lord. You will cross the day of your death by the grace of the Lord, which is a rebirth. Such extension of life will help you really in the spiritual effort if you are given a human rebirth there will be lot of gap since you have to stay in the womb of your mother and you have to cross the childhood. Such long gap will give a serious break in your spiritual effort.
From this point of view also there is no human rebirth. If one cannot attain the Brahmaloka in this human birth itself by getting the extension of life, can such a soul get Brahmaloka in the next human birth after such a long gap? Gita also says that the soul is taking birth and death constantly during the day and night (Athachainam Nitya Jatam). Like this all the three religions can be correlated and only one theory is evolved.