Why is there suffering in the world? More specifically, why does the Torah give the tochacha, the list of all the curses that will afflict the people if they do not keep the Torah properly?
In this world, we have a body and a soul. The Yetzer Hara – the evil inclination – exists in the soul, and the Yetzer Tov – the positive inclination – exists in the body. Ideally, אִם בְּחֻקֹּתַי תֵּלֵכוּ וְאֶת מִצְוֹתַי תִּשְׁמְרוּ – the soul transcends the physical of the world, and the person becomes separate from the world, different, holy.
However, אִם בְּחֻקֹּתַי תִּמְאָסוּ – if the body sins, it comes to the fore, and it supersedes the soul, to the point where soul is almost strangled, as it were. If the soul were to die, the body would be no different to that of animal – lead by sense and impulse.
Suffering is an emergency safety measure that kicks in to avoid this. It minimises the physicality the body partakes in. It prevents the body from getting addicted to what will eventually destroy the soul. In this way, suffering cleanses us.
This applies to all suffering, including the Holocaust.
The victims were martyrs. Whatever they were in life, they were קדושים, holy martyrs, in death. They died על קידוש ה. The Gemara in Sanhedrin explains that in dying על קידוש ה, the victim becomes a figurative and actual korban, a sacrifice. All suffering is smaller degree of this, all suffering is in some way a קרבן לה. The Bluzhever Rebbe used to tell people to get a bracha from a Holocaust survivor for the very same reason.
All suffering reduces the domination of body over soul, of matter over mind,
People usually suffer most in their old age, toward the end of their lives. This is when they are older, and thus free from the sins of their youth. Hashem postpones suffering in the elderly in order that the person may greet his Creator in the most pure and direct way.
Parshas Behar and Bechukosai frequently appear together – Behar teaches about the Torah at Sinai, and Bechukosai is the blessings and curses. R’ Yaakov Minkus explains that they are together because they both take us to Har Sinai – Torah and suffering both.
Suffering removes the framework the Yetzer Hara operates and thrives in. It brings a person closer to Sinai and Hashem by breaking the hold his body has over his soul, purifying and cleansing him.