Faith is a fun subject to discuss in Buddhism, because it seems that everyone has a different interpretation, and how it relates to their past experience with religion. People who leave other religions for Buddhism often have a negative interpretation of faith, while people who grew up Buddhist might see faith as a given and something that just comes with the territory.
In the famous introduction to Buddhism, What the Buddha Taught, the author Walpola Rahula talks about this subject in the first chapter:
The Buddha went even further. He told the bhikkhus that a disciple should examine even the Tathāgata (Buddha) himself, so that he (the disciple) might be fully convinced of the true value of the teacher whom he followed. (pg. 3)
Indeed, this is mentioned in a sutra in the Pali Canon called the Vīmaṁsaka sutta (MN 47) which unfortunately isn’t translated on Access to Insight, but fortunately I do have a copy of Bhikkhu Bodhi’s The Middle Length Discourses of the Buddha: A Translation of the Majjhima Nikaya which does contain the sutra.
The Vimamsaka Sutta begins with the Buddha saying to his bhikkhu (monastic) disciples:
“Bhikkhus, a bhikkhu who is an inquirer, not knowing how to gauge another’s mind, should make an investigation of the Tathāgata (Buddha) in order to find out whether or not he is fully enlightened.
He then instructs the disciple to use their eyes and ears to discern if the Buddha manifests any defiled states of behavior, any “iffy” states of behavior, and finally any wholesome states of behavior and in particular if he has consistently shown wholesome states of behavior for a long time (i.e. not just recently).
Further, things the Buddha encourages the disciples to examine are the Buddha’s track record, his conduct: does he live without fear? is he well behaved? is his reputation clean without a hint of concern?
If so, the sutra instructs that it is safe to approach such a teacher, to hear his teaching and to put it into practice.
Finally, at the end of the sutra, the Buddha says:
“Bhikkhus, when anyone’s faith has been planted, rooted, and established in the Tathāgata through these reasons, terms and phrases, his faith is said to be supported by reasons, rooted in vision, firm; it is invincible by any recluse or brahmin or god or Māra or Brahmā1 or by anyone in the world. That is how, bhikkhus, there is an investigation of the Tathāgata in accordance with the Dhamma, and that is how the Tathāgata is well investigated in accordance with the Dhamma.”
Thus, faith in Buddhism is somewhat different than other religions in that Buddhism should be thoroughly investigated first, and only then will confidence and faith arise if proven to be true. If it can’t stand the “acid test”, it shouldn’t be followed. Even if someone has been Buddhist a long time, there’s nothing wrong with taking a step back and asking yourself “should I really be following this?” and then using the eye of discernment to thoroughly investigate the Dharma, and the life of the Buddha as a manifestation of that Dharma.
1 These are two of the many gods in the ancient “Vedic” religion of India in the time of the Buddha, the forerunner to what we call Hinduism today. Māra was the primary antagonist in early Buddhism as a kind of deceiver god, while Brahmā was a creator god, and protector of Buddhism.