Question: Must people know who Amitabha is for the recitation to be effective, or does it have power regardless?
Response: To attain rebirth in the Pure Land, we need to have faith, vows, and practice. Basically, faith means that we believe what the Buddha taught us, vows means that we make the vow to be reborn in the Pure Land, and practice means we live a moral life and chant “Amituofo.”
Sakyamuni Buddha told us that at the end of the Dharma-ending age, the age we are now in, as his teachings are gradually lost to us; the last sutra to remain will be the Larger Amitabha Sutra, also called the Infinite Life Sutra. This sutra “will remain for another hundred years to rescue sentient beings and lead them to the Western Pure Land.” After that, only the name of Amitabha Buddha will remain for a final one hundred years.
From this, we can see that just chanting “Amituofo” benefits us. How much depends on our good roots, good fortune, and causal conditions. But, at the very least, chanting “Amituofo” will plant more seeds in our Alaya (most subtle) consciousness. So while we do not know when we will benefit from our chanting, we can be assured that at some time we will.
For our sake—and the sake of all those we have vowed to help—the sooner we attain the ultimate benefit and achieve rebirth in the Pure Land, the better.