Buddhist teachings can be applied to everyone’s daily life, provided that one should have the right dharma knowledge.[quoteWell, I was lost at the second sentence. What exactly does "Buddha manifested as a human being" mean?[/quote]
In Buddhist teachings, all existence (beings) are categorized into the three realms – the desire-realm, the form-realm, and the formless-realm.
The desire-realm, where we stay in, consists of (1) mankind, (2) animals, (3) asuras, (4) hungry spirits, (5) hell, and (6) the six heavens paths. So called because the beings in these state are dominated by desires, in general, one’s consciousness is subject to the desires for food, sex, and sleep. During our transmigrations of rebirths, we don’t always manifest as a human, we could be a heavenly being or as an animal.
That’s the meaning of “…manifested as a human being,” in the Sutras, the Buddha did tell many stories about his countless past lives as a heavenly being or an animal, and he had always seek to the cultivation of the ultimate truth.
In fact, as a human, we are considered to be the best path for Buddhist cultivation, if we could go further on this thread in the future, you will automatically find out why.
Are you exactly the same person (in every way) as five minutes ago? Before you read my reply, you didn’t know what I am going to say, right? Meanwhile you might gasp at the content, your metabolic systems function without your notice. Your thoughts keep changing every instant. This is an unceasing births-and-deaths happening within the small scope of your own perception, you are never the same one when you observe deeply and subtly. Another example, have you ever got a certain experience of déjà-vu? A certain place, a smell of fragrance, a certain coloring, a piece of music…, it brought forth an indescribable tone of something, though, not knowing what it was. This is the result of your past experiences which was brought forth by your seventh vijnana from the Buddha nature (the Alaya vijnana) without your control (the third round of the dharma transmission by the Buddha).
Even now, you have the interest and made an effort to read the thread and ask questions, this deed was also influenced by your past life experiences that you must have got involved with Buddhism before. The most obvious case of the talented Mozart, he must have been a musician in his many past lives as well. This is all because everyone’s Buddha nature (the Alaya vijnana) serves as a storage space for all our deeds, and the Alaya vijnana is eternity, it never ceases to function.