To understand the necessity of suffering, we have to start with why it’s possible in the first place.
The highest purpose for which we were created was to enter into a loving relationship with the Lord and to worship him. However, that kind of relationship requires a free will choice on our part. Because love is, by nature, a choice more than an emotion, if God forced it from us, then it would cease to be love. And we can know that’s the case, in part, because otherwise there is no good reason for him to have created us with free will.