Question: Some teach many mantras for practice in everyday life for various purposes. Do I have to practise them all?
Answer: If these mantras were taught without clear researchable authentic sutra sources for reference, it is best not to practise them. It is worth noting that the name of Amitabha Buddha (Amituofo) is already a supreme mantra, as can be seen at http://purelanders.com/2011/12/16/the-name-of-amituofo-is-the-supreme-mantra
Amituofo’s name can be chanted for various purposes too, including protection, healing and reaching his Pure Land. The truth is, Sakyamuni Buddha did not teach many mantras while expecting us to master all of them in this lifetime, as it would be difficult, if not impossible for most to recall every single one for every occasion.
The Buddha taught many different mantras as many means to reach out to many different beings with various karmic affinities. While the chanting of many mantras is surely good, it is important to focus on one for one’s Main Practice. As all mantras are interconnected to the essence of the Dharma, sticking to one with a clear understanding will do.
Note too, that most beings already by default have the most affinity with Amituofo, which is why all Buddhas will teach about him and his Pure Land. Once his Pure Land is reached, as in the 34th vow of Amituofo, ‘all profound dharanis’ (诸深总持) will be realised there. (Dharanis are extended mantras which contain the essence of interconnected teachings.) Without focused practice, not only will his Pure Land not be reached, it will also take much longer time to master all dharanis.