Suffering has replaced the offerings that the Jewish people would bring when the Temple in Jerusalem was standing. The goal of suffering is to cleanse a person of his sins in this world and save him from punishment in the World to Come. There is an additional reason for suffering. If someone did not suffer at all in this world, it would be as if he received, in this world, the full reward for his good deeds. God therefore brings lower intensity suffering in this world so we can receive our true reward in the next.

Suffering brings atonement now that the Temple is destroyed and we no longer bring offerings:

Why are they referred to as “sufferings of love” (Berakhot 5a)? Did we not explain above that suffering [in this world is understood as] punishment for the few sins he did [and therefore should be considered “judgment” and not “love”]?… Even so, one who sinned unknowingly does not deserve to be punished in Gehenna and in the “well of destruction” for his error. Rather, he must be cleansed of that sin, and sanctified and purified, in order to make him fit for the level in the World to Come that is appropriate for his good deeds. Therefore, the Holy One, blessed be He, had mercy on His nation and His pious ones, and gave them [the commandment to bring] offerings to atone for sins done unknowingly. When, [as in our times,] the Temple is not standing, He sends them suffering in order to cleanse them of those unknowing sins.... As such, this suffering is an expression of God’s love and compassion for a person.

Minor suffering comes to save a person from losing his reward in the World to Come:

Our Sages also mentioned another approach to suffering. They said: “In the academy of Rabbi Yishmael they taught: Anyone who went forty days without suffering has [already] received his [reward in this] world [as opposed to the World to Come]” (Arakhin 16b). The explanation is as follows: There are things that naturally happen to a person, like occasional inconveniences, bodily pain from eating spoiled food, or getting a headache from exposure to the sun. These are bothersome parts of life that even happen to kings. The only person who is saved from these [minor troubles] is the evil person who is destined for Gehenna and receives his reward in this world. Heaven makes sure that such a person is able to get whatever he wants in this world [in order to be punished fully in the next]. (Ramban, Torat HaAdam, Sha’ar HaGemul)

God wants the best for man. As such, when He brings man suffering His intent is to heal the sickness in his soul and to remind him to change his evil ways. If a person does not internalize this message, he ends up being punished twice, once in this world and once in the next. But when he is receptive to the divine message, he should be happy and thankful for the suffering he experienced.

You should know that God’s reproof [through suffering] is for man’s good. For if a man sins before Him and does something wrong in His eyes, God’s reproof accomplishes two things: One is to atone for his sins and remove his iniquity…. It is through the body’s sickness that the soul’s sickness is healed, for sin is a sickness of the soul…. The second [goal of divine reproof] is to remind a person to repent from his evil ways. But if he does not internalize the reproof, nor humble himself as a result of the rebuke, and does not make a true internal transformation, woe to him and woe to his soul. For he endured suffering and bore punishment for his sin, yet his sin was not atoned for – and he ends up receiving double the punishment [in this world and the next]. But when a person is receptive to the divine reproof and improves his character and behavior [as a result], he should be happy about his suffering, for it benefited him immensely in many lofty ways. The suffering is a cause to thank God, may He be blessed, just like any other success [in life]. (Rabbeinu Yona Gerondi, Sha’arei Teshuva 2:3–4)

Further reading: For more on reward and punishment, see p. 256.

Suffering is also divine goodness which comes from above. In fact, it stems from a higher spiritual level than revealed goodness. Suffering, which appears in this world to be darkness, actually comes from a hidden lofty divine revelation, an extremely high divine light.

The Sages offer sound advice to clear one’s heart of any sadness or nagging worries about mundane matters, or even [difficulties with] children, health or livelihood…. [Accept with joy] that this is also good. Its benefit is just not apparent to mortal eyes, since it emanates from the concealed world, which is higher than the revealed world. (Rabbi Shneur Zalman of Liadi, Tanya, Likutei Amarim 26)

Every individual must connect with God through his own personal type of spiritual service. As such, the suffering a person endures is connected to his own spiritual level. Suffering also illuminates a person’s soul and diminishes the importance of his body and materialism in his life. So one who undergoes suffering is purified and cleansed, and can be a positive influence on many others.

The suffering each person experiences fits his own particular soul and the way he as an individual is supposed to serve God:

Everyone experiences suffering according to his own soul and his own particular divine service. One person suffers because of his children or a parent or neighbor. Another, on a higher level, suffers [even] from distant neighbors. Another, even greater, suffers from anywhere in the city. And there are those who are very great who suffer from the entire world.

Suffering empowers the soul:

Anyone who suffers from particular people [in a sense] “carries” those people, for when he suffers from them he carries them upon himself. But how can a [limited] physical being carry so many people? [The process is as follows:] Through suffering his body becomes submissive – for all suffering is referred to as tzarot (troubles) because it constricts (metzirin) and oppresses the body. When the body is crushed through troubles, the soul shines and grows – for when [man’s] physical [side] is subdued, his spiritual form (tzura) grows…. The word tzara (trouble) is related to the word tzura (spiritual form), for through tzarot (troubles) the tzura (spiritual makeup) grows. It follows that through suffering and troubles a person’s spiritual form – his soul – grows. [Because it grows] it is now able to carry on it a large number of people. (Rabbi Naĥman of Breslov, Likutei Moharan 170)

Further reading: For more on the value of suffering, see A Concise Guide to the Sages, p. 256.