According to Sanatan Hindu texts, the soul leaves the body as soon as a person dies. Hindus do not believe in bodily resurrection and they give no importance on preserving the corpse as death is spiritually viewed as an escape from one life to an ultimate moksha(nirvana), shanti(peace) and parampada(the ultimate place). So cremation is usually seen in Hindu funeral rituals.
Hindus believe that the soul is eternal, ever-existing and primeval; the death symbolizes the end of the existence of a person’s physical being and the start of a new journey for the soul. This soul then reincarnates in some other material body form, and passes through the same cycle of taking birth, growing and finally meeting death. In the BhagavadGita(2.20) the Lord says, “For the soul there is neither birth nor death at any time. He has not come into being, does not come into being, and will not come into being. He is unborn, ever-existing and primeval. He is not slain when the body is slain.”
In Hinduism it is said that a person’s body is composed of Pancha Mahabhootas (5 elements)- Dhara(earth), Agni(fire), Varuna(water), Vayu(air) and aakasha(sky) and among these Agni (fire) is the only element which can absolutely purify and merge the body again with Pancha Mahabhootas. So, Hindus cremate the dead bodies except the dead bodies of babies, children, and saints and chant the Mantra of Antyeshtikriya, ‘divyan lokan sa gacchatu (May Thy soul transpire to Heavenly bodies)’. Cremation is also scientific. We know that soil, water, air and sky all can be polluted but fire can never be polluted.
So, tradition of cremation is undoubtedly hygienic and scientific.