A man fulfills the negative mitzvah of not having relations with his sister perfectly - he never even thinks about doing it. This is because he has no sister. Does he get credit for this?
I would think not, since there is no effort involved in refraining from performing the action. But there is no effort in having a bris milah when one is a baby and one gets credit. So I am not sure.
This is equivalent to asking about doing the mitzvot we can't do today, such as because we have no Temple or Sanhedrin.
The answer from Menachot 110a (see Shulchan Aruch Harav, Orach Chaim 1:9) is that we get credit for doing them by studying them.
Also, by the fact that we are all connected on the highest levels, and are all responsible for one another, we fulfil them through proxy for eachother.
Some say we fulfil them all over up to four reincarnations.
We may not get a rock solid answer to this. We have to hope and trust that Hashem puts as much effort into finding ways to credit us, as He promises to find ways to overlook our sins and forgive us.
Thanks for the really good question and may we all be successful in fulfilling the mitzvot as best we can.
You get credit for all mitzvot fulfilled, regardless of how much work it takes. However, as Ben He He said in the Mishnah, the reward will be greater if the effort expended is greater. [Avot 5:21]
In Vayikra 18:5, it says:
You shall therefore keep my statutes, and my judgments: which if a man do, he shall live in them: I am the L-rd.
The Gemara in Makkos 23b elaborates on this, and explains that:
[...] with regard to one who sits and did not perform a transgression, G-d gives him a reward like that received by one who performs a mitzva.
