Chullin 142 - Reward for the Mitzvot
One may not take the mother bird while on her young even if he needs her to purify the leper and allow him to enter the Temple. This is true even though he wants to send her away as part of the purification ritual. By sending the bird away he loses a small amount of money, and still the Torah promised "that it will be good for you and you will live long." How much more so does this apply to the difficult commandments of the Torah.
Rabbi Yakov said that "good and long life" can only mean the next world, not this one. In fact, the mention of the reward is itself a proof of the resurrection of the dead, because only in the next world is the true reward possible. For if you don’t say so, what about a son whom his father asked to send away the mother bird, and while performing this mitzvah and respecting his parent, for which long life is promised, he fell from the tree and died?
But perhaps such an incident could never happen? - Rabbi Yakov saw it. But perhaps he had bad thoughts? - God does not count bad thoughts as deeds. But perhaps he was thinking about idol worship, where thoughts are counted as deeds? - The mitzvahs should have protected him from such thoughts. Since they did not, this proves that there is no reward for them in this world.
But how could he die while performing a mitzvah; those sent to perform a mitzvah are not harmed, even on the way back!? - The ladder was shaky, and in a place of danger this rule does not work. Acher, the famous Sage turned bad, was the grandfather of Rabbi Yakov. Had he heard his grandson’s explanation, he might not have sinned: "so that it will be good with you" refers to a world that is truly good, and "so that your days will be prolonged" refers to life in a world that is truly long.
Art: Giovanni Battista Tiepolo - The entrance to a large barn, a ladder leaning against the wall to the left