Mishnah 7. This mishnah returns to the subject we dealt with in mishnayos 3 and 4 - the principle of presuming a person to be alive - and continues to apply it to a further case.
The case in the mishnah:
A person lent money to a kohen, to a Levi or to a poor man, and stipulated with them that the loan would be repaid in the following manner: he would separate from his produce the gifts due to them - Terumah to the kohen, the first tithe to the Levi and the poor man's tithe to the poor man - and keep them for himself as payment against the debt.
The mishnah rules that he may go on separating on their behalf "b'chezkas she'hen kayamin" - on the presumption that they are still alive - and he need not be concerned about three possibilities:
Perhaps the kohen has died.
Perhaps the Levi has died.
Perhaps the poor man has become wealthy and is no longer poor.
What these concerns mean:
Had the kohen or the Levi died, the lender would need to obtain permission from the heirs in order to continue repaying the debt in this way, by taking the Terumah and tithes for himself. For they are not obligated to agree to it: once the debt has passed to them, they may well prefer to be paid in cash.
So too with the poor man: if he has become wealthy, he is no longer entitled to the poor man's tithe and to the gifts of the poor, and his debt can no longer be repaid in that same way.
Regarding all of these, the mishnah teaches that there is no need for concern. One is permitted to assume that the kohen and the Levi are still alive and that the poor man is still poor, and to continue separating as usual.
If they actually died:
If the kohen or the Levi did in fact die, the presumption no longer suffices, and the lender must obtain permission from the heirs in order to continue separating the Terumah and tithes on their behalf.
A loan made before beis din:
However, if the arrangement - that the debt would be repaid by taking the Terumah and tithes - was made before beis din and on this condition, the lender does not need the heirs' permission even after the death of the kohen or the Levi. Beis din has the authority to establish that the arrangement remains in force until the loan is repaid in full.
In summary: In this mishnah we learned a further application of the principle of presuming a person to be alive - one who lends money to a kohen, to a Levi or to a poor man in order to separate their gifts on their behalf separates on the presumption that they are alive, and need not be concerned that perhaps they died or that perhaps the poor man became wealthy. If they actually died, he must obtain permission from the heirs; and if the loan was made before beis din, he need not obtain permission, for the authority of beis din keeps the arrangement in force until the debt is repaid.