Do you have to believe in rebirth, other worlds and post-mortem kamma to practise Buddhism?
New question - under review
To begin, no - the suttas ask for no oath at the door. But the reverse is false too: rebirth and kamma are built into the early teaching, and they cannot be pulled out without damaging the structure.
MN 95 shows how the canon handles belief. The young brahmin Kāpaṭhika raises the question of the Vedic tradition, which the brahmins hold to be the only truth. The Buddha introduces the “safeguarding of truth” (saccānurakkhaṇā): if you have faith (saddhā), it is honest to say “such is my faith” and stop there - but not to add “only this is true, everything else is false”. The same holds for preference (ruci), oral tradition (anussava), reasoning (ākāraparivitakka) and a view accepted after reflection (diṭṭhinijjhānakkhanti). None of the five grounds licenses that certainty. The same sutta then lays out a long sequence: the student first examines the teacher himself for greed, hate and delusion, and only then come trust, listening, memorising, examining the meaning, considered acceptance, zeal, application, weighing - and only at the end the personal realisation of the ultimate truth. Saddhā here is trust after inspection, an advance against work to be done, not a finished answer.
MN 60 is blunter. The brahmin householders of Sālā admit they have found no teacher they trust, and the Buddha sets out the apaṇṇaka dhamma, the incontrovertible teaching. He does not stay neutral: there is another world, and denying it is called wrong view. But the argument he develops is a pragmatic one. From someone holding the nihilist view - no gift, no fruit of good and bad actions, no other world - bad conduct of body, speech and mind is to be expected; he is blamed here already, and if there is another world, he loses there as well. The one who holds the opposite wins either way. AN 3.65, the discourse to the Kālāmas of Kesaputta, makes a similar move: a noble disciple (ariyasāvaka) who has cleared his mind of hostility and ill will gains four assurances. The first two say his position holds up whether or not there is another world with fruit of action. The other two are conditional: if evil comes to the one who does evil, then no suffering threatens him, who does none; and if it does not, he is pure either way.
This is not reducible to “believe just in case”: the wager argument sits next to the Buddha’s plain statement that there is another world. But it cuts both ways. For someone who does not know and does not see, “there is definitely nothing after death” is an equally unproven claim, and it is not free - it changes what a person finds it reasonable to do.
Rebirth will not come out of the text either. MN 117 distinguishes two kinds of right view. The mundane kind (sāsavaṃ puññabhāgiyaṃ upadhivepakkaṃ - “affected by taints, partaking of merit, ripening in the acquisitions”) spells it out: there is what is given and what is offered, there is fruit of good and bad actions, there is this world and the other world, there is mother and father, there are beings reborn spontaneously, there are ascetics who have realised both worlds themselves. The second kind, noble and supramundane, is a factor of the path, the wisdom that discriminates. Kamma, meanwhile, is in the suttas first of all intentional action (cetanā), and some of its results are visible in this life, not only after it.
An honest secular position sounds roughly like this: I do not know what happens after death, I assert neither answer, and I work with what I can check - greed, hate, attention, actions and their consequences now. You can practise that way, and MN 95 defends such caution. But caution is not yet the whole of right view, and the four truths are not confined to one life: suffering there is defined through birth, ageing and death, and the goal is the ending of further becoming. Early Buddhism is not neutral about rebirth, and making it neutral is no longer reading - it is editing.
Where to read: MN 60, MN 95, MN 117.