The reason for the concealment of the face from the people has been explained: it is deliberately to give people room for labor and engage in His work in Torah and Mitzvot out of choice. This is because this increases the contentment of the Creator from their work in His Torah and Mitzvot more than His contentment from His angels above, who have no choice and whose work is coerced.
“Introduction to The Study of the Ten Sefirot,” Item 80
That deficiency was born only out of the concealment of the face of the Creator, who did not wish to shine His face upon His creatures from the start, so they would be complete from the start. On the contrary, He hid His face from them and left them lacking, since here is the Light of the King’s face is certainly life, and its concealment is the source of every evil.
However, the purpose of this concealment is not to be concealed. On the contrary, it is to be revealed later and to transform any evil born only out of that concealment. Thus, He established law and order to reveal the face of His concealed benevolence through people's actions. These are the laws and the doctrines which He gave to us. His law is the law of truth, which if a man does, he shall live by them, in the eternal life, for the reward of a Mitzva [commandment/good deed] is a Mitzva. This is the illumination of His face, which He concealed from man in the beginning of His Creation.
Thus, for toil he was created, since the inclination governs him and his evil is great in all kinds of faults, along with his remoteness from the Light of life. And the practice of Mitzvot shine the hidden Light upon him until, when he completes his Mitzvot, he himself is complemented with them into Light, in the Light of this life.
Ramchal, Daat Tevunot (Knowledge of Intelligence)
Had he told them about the wondrous things in the essence of the reward, they would necessarily use and assume His work in order to obtain that wonderful reward for themselves. This would be considered working for themselves, for self-love. That, in turn, would falsify the whole purpose.
Baal HaSulam, “The Arvut [mutual guarantee],” Item 29
The Creator is surely the epitome of goodness. Indeed, it is the law of the good to do good, and that is what He desired—to create creatures so He could do good to them, for if there is no recipient of the goodness, then there is no benevolence. Yet, for the benevolence to be complete, He knew in His sublime wisdom that the recipients should receive it through their own toil, for then they would own that goodness and they will not be ashamed when receiving the goodness, as with one who receives charity from another.
Ramchal, Daat Tevunot (Knowledge of Intelligence)
For the creatures to receive the delight and pleasure, and to avoid shame upon the reception of the pleasure, a correction was made. The correction is restriction and concealment of the Upper Light. This means that before one receives the correction on the will to receive so that it is in order to bestow, there is no disclosure of Upper Light. For this reason, we cannot feel the taste of the Mitzvot [commandments] that we keep, which should have given us the taste of delight and pleasure, meaning to avoid the sense of shame upon the reception of the pleasure. This is the reason why there was a correction called “having to aim in order to bestow upon the reception of the pleasure,” otherwise concealment lies upon the deeds.
Rabash, Rabash—the Writings of Rabash,
“What Are Holiness and Purity, in the Work”
All is set with ahead of time and each and every soul is already in all its Light, goodness, and eternity. It is only for the bread of shame that the soul came out restricted until it clothes in the murky body, and by its power does she return to her root prior to the restriction, with her rewarded from the whole of the terrible journey that she performed. And the entire reward is the real Dvekut [adhesion]. This means that she was rid of the bread of shame because her vessel of reception has become a vessel of bestowal and her form is equal to her Maker’s.
Baal HaSulam, Letter no. 25