Kamma is not a matter of faith, it is something to be be investigated and understood.
"'Kamma should be known. The cause by which kamma comes into play should be known. The diversity in kamma should be known. The result of kamma should be known. The cessation of kamma should be known. The path of practice for the cessation of kamma should be known.' Thus it has been said. In reference to what was it said?
"Intention, I tell you, is kamma. Intending, one does kamma by way of body, speech, & intellect.
"And what is the cause by which kamma comes into play? Contact is the cause by which kamma comes into play.
"And what is the diversity in kamma? There is kamma to be experienced in hell, kamma to be experienced in the realm of common animals, kamma to be experienced in the realm of the hungry shades, kamma to be experienced in the human world, kamma to be experienced in the world of the devas. This is called the diversity in kamma.
"And what is the result of kamma? The result of kamma is of three sorts, I tell you: that which arises right here & now, that which arises later [in this lifetime], and that which arises following that. This is called the result of kamma.
"And what is the cessation of kamma? From the cessation of contact is the cessation of kamma; and just this noble eightfold path — right view, right resolve, right speech, right action, right livelihood, right effort, right mindfulness, right concentration — is the path of practice leading to the cessation of kamma.
"Now when a disciple of the noble ones discerns kamma in this way, the cause by which kamma comes into play in this way, the diversity of kamma in this way, the result of kamma in this way, the cessation of kamma in this way, & the path of practice leading to the cessation of kamma in this way, then he discerns this penetrative holy life as the cessation of kamma.
"'Kamma should be known. The cause by which kamma comes into play... The diversity in kamma... The result of kamma... The cessation of kamma... The path of practice for the cessation of kamma should be known.' Thus it has been said, and in reference to this was it said."
As for rebirth, the Buddha did not command belief and he knew there was no "logical proof" he could provide for the phenomenon... rather he showed the consequences that could arise from a lack of belief in some form of post-mortem continuation.
A. "There are some brahmans & contemplatives who hold this doctrine, hold this view: 'There is nothing given, nothing offered, nothing sacrificed. There is no fruit or result of good or bad actions. There is no this world, no next world, no mother, no father, no spontaneously reborn beings; no priests or contemplatives who, faring rightly and practicing rightly, proclaim this world and the next after having directly known and realized it for themselves.'1
B. "Some brahmans & contemplatives, speaking in direct opposition to those brahmans & contemplatives, say this: 'There is what is given, what is offered, what is sacrificed. There are fruits & results of good & bad actions. There is this world & the next world. There is mother & father. There are spontaneously reborn beings; there are priests & contemplatives who, faring rightly & practicing rightly, proclaim this world & the next after having directly known & realized it for themselves.'
"What do you think, householders? Don't these brahmans & contemplatives speak in direct opposition to each other?"
"Yes, lord."
A1. "Now, householders, of those brahmans & contemplatives who hold this doctrine, hold this view — 'There is nothing given, nothing offered, nothing sacrificed. There is no fruit or result of good or bad actions. There is no this world, no next world, no mother, no father, no spontaneously reborn beings; no priests or contemplatives who, faring rightly and practicing rightly, proclaim this world and the next after having directly known and realized it for themselves' — it can be expected that, shunning these three skillful activities — good bodily conduct, good verbal conduct, good mental conduct — they will adopt & practice these three unskillful activities: bad bodily conduct, bad verbal conduct, bad mental conduct. Why is that? Because those venerable brahmans & contemplatives do not see, in unskillful activities, the drawbacks, the degradation, and the defilement; nor in skillful activities the rewards of renunciation, resembling cleansing.
A2. "Because there actually is the next world, the view of one who thinks, 'There is no next world' is his wrong view. Because there actually is the next world, when he is resolved that 'There is no next world,' that is his wrong resolve. Because there actually is the next world, when he speaks the statement, 'There is no next world,' that is his wrong speech. Because there actually is the next world, when he is says that 'There is no next world,' he makes himself an opponent to those arahants who know the next world. Because there actually is the next world, when he persuades another that 'There is no next world,' that is persuasion in what is not true Dhamma. And in that persuasion in what is not true Dhamma, he exalts himself and disparages others. Whatever good habituation he previously had is abandoned, while bad habituation is manifested. And this wrong view, wrong resolve, wrong speech, opposition to the arahants, persuasion in what is not true Dhamma, exaltation of self, & disparagement of others: These many evil, unskillful activities come into play, in dependence on wrong view.
A3. "With regard to this, a wise person considers thus: 'If there is no next world, then — at the break-up of the body, after death — this venerable person has made himself safe. But if there is the next world, then this venerable person — on the break-up of the body, after death — will reappear in the plane of deprivation, the bad destination, the lower realms, in hell. Even if we didn't speak of the next world, and there weren't the true statement of those venerable brahmans & contemplatives, this venerable person is still criticized in the here-&-now by the wise as a person of bad habits & wrong view: 2 one who holds to a doctrine of non-existence. If there really is a next world, then this venerable person has made a bad throw twice: in that he is criticized by the wise here-&-now, and in that — with the break-up of the body, after death — he will reappear in the plane of deprivation, the bad destination, the lower realms, in hell. Thus this safe-bet teaching, when poorly grasped & poorly adopted by him, covers (only) one side, and leaves behind the possibility of the skillful.
B1. "Now, householders, of those brahmans & contemplatives who hold this doctrine, hold this view — 'There is what is given, what is offered, what is sacrificed. There are fruits & results of good & bad actions. There is this world & the next world. There is mother & father. There are spontaneously reborn beings; there are priests & contemplatives who, faring rightly & practicing rightly, proclaim this world & the next after having directly known & realized it for themselves' — it can be expected that, shunning these three unskillful activities — bad bodily conduct, bad verbal conduct, bad mental conduct — they will adopt & practice these three skillful activities: good bodily conduct, good verbal conduct, good mental conduct. Why is that? Because those venerable brahmans & contemplatives see in unskillful activities the drawbacks, the degradation, and the defilement; and in skillful activities the rewards of renunciation, resembling cleansing.
B2. "Because there actually is the next world, the view of one who thinks, 'There is a next world' is his right view. Because there actually is the next world, when he is resolved that 'There is a next world,' that is his right resolve. Because there actually is the next world, when he speaks the statement, 'There is a next world,' that is his right speech. Because there actually is the next world, when he is says that 'There is a next world,' he doesn't make himself an opponent to those arahants who know the next world. Because there actually is the next world, when he persuades another that 'There is a next world,' that is persuasion in what is true Dhamma. And in that persuasion in what is true Dhamma, he doesn't exalt himself or disparage others. Whatever bad habituation he previously had is abandoned, while good habituation is manifested. And this right view, right resolve, right speech, non-opposition to the arahants, persuasion in what is true Dhamma, non-exaltation of self, & non-disparagement of others: These many skillful activities come into play, in dependence on right view.
B3. "With regard to this, a wise person considers thus: 'If there is the next world, then this venerable person — on the break-up of the body, after death — will reappear in the good destination, the heavenly world. Even if we didn't speak of the next world, and there weren't the true statement of those venerable brahmans & contemplatives, this venerable person is still praised in the here-&-now by the wise as a person of good habits & right view: one who holds to a doctrine of existence. If there really is a next world, then this venerable person has made a good throw twice, in that he is praised by the wise here-&-now; and in that — with the break-up of the body, after death — he will reappear in the good destination, the heavenly world. Thus this safe-bet teaching, when well grasped & adopted by him, covers both sides, and leaves behind the possibility of the unskillful.
Retro.