Let me clarify a bit concerning your question, “What is decoration at the point of desire,” which you said was difficult for you to understand.
To understand the meaning of decoration we must first understand to what things are referring, meaning what is perplexing to him and what he wants to explain.
We know that there are only two things in the world: Creator and creatures. This means that the Creator wants to bestow pleasures upon the creatures, as it is written, “His desire to do good to His creations.” Out of that discernment, the first world that emerged is called “the world of Ein Sof [no end],” which means that since He desires to do good, He has created “existence from absence” a desire to receive the pleasure that He wants to give.
Of course, that desire was precisely the size suitable for reception of all the light, for otherwise, meaning if the Kli [vessel] is smaller than the light, the creature will not emerge whole, and the certainly Creator created something whole, meaning that He has created a desire to receive that specific light that He has allocated for the creatures.
And according to that desire, the light extended and filled it completely. This is regarded as the upper light filling the whole of reality, which is why it is called Ein Sof, since the will to receive did not put a stop and conclusion on the light, but rather expanded into the vessel of reception. That is, had that discernment been drawn back, there would have been no room where Godliness were felt in the world. Even when Adam was immersed in the lust for reception of pleasures only for himself, he still felt Godliness. Only once the Tzimtzum [restriction] on receiving with the intention for oneself alone took place, it came about that one who is immersed in lust does not feel Godliness and the beginning of one’s work is to believe that there is Godliness in the world. This is so only because of the concealment that was done by the Tzimtzum.
We learned that in the world of Ein Sof, “it came up in His will … and He restricted Himself.” He interprets that by this he means that there was an ascent of the desire, since the will to receive is opposite from the desire to bestow, which is why he chose more Dvekut [adhesion]. Dvekut means equivalence of form, and he wanted to be similar to the giver, so he restricted himself. This means that in Ein Sof there seems to have been oppositeness between the Kli and the giver to the point that He had to correct it, and that for this correction he had set up the Tzimtzum.
He introduces Pirkey de Rabbi Eliezer, where it is written that before the world was created there was “He and His name are one.” This means that there was no difference between the light, which is called “He,” and “His name,” which is the Kli, meaning the will to receive. He interprets that the Kli is called “His name” because Shmo [His name] in Gematria is Ratzon [desire]. But according to this, it is perplexing, for if there were no oppositeness between the Kli and the light, why was there a need to perform a correction that there will be equivalence, to the point that for this reason he performed the Tzimtzum? This is why he explains that this correction was not due to a lack, where he felt that there was oppositeness, but in order to decorate.
We can understand the difference between decoration and a lack through an allegory. A town’s rabbi made a convention and sent for all the wealthy and respectable people in town to gather in the synagogue, for he wanted to tell them something. The rabbi came on stage and gave a heartfelt sermon about the greatness and importance of charity. Afterwards he told them that since and good man, a wise disciple, has just arrived from overseas, and he had children and a family of eight, and they did not have food for even one meal, no place to stay, and the family is now in the women’s section of the synagogue, so he would like each one to donate even more than he can because it is really a matter of life and death, as they have no place to stay. And the rabbi wept bitterly.
Naturally, the people of Israel are all merciful and each one gave more than he could, and he collected thousands of pounds for that family, since everyone felt the lack, and therefore everyone took part in mending the lack that they felt.
The following year, the rabbi assembled the town’s powerful and respectable and gave them another heartfelt sermon, and cried and sighed so bitterly that it could break one’s heart. He let them know the merit of the Mitzva [good deed/commandment] of mercy—that through mercy we will come out of exile and be rewarded with complete redemption.
Afterwards he told them that his wife was at a wedding of a rich man who came from the United States, and she saw there that the rich man’s wife wore a costly fur that costs 3,000 pounds, and a diamond ring that costs another 3,000 pounds, so now she is asking him to buy her these Jewels for 6,000 pounds. The rabbi wept bitterly and asked for them to have mercy on him and give him that amount. He would not have asked them for it had he not seen that last year they gave him 6,000 pounds for the poor man so he could get by with his family, and it must be because they have merciful hearts, so he is asking them for that amount for Jewels for his wife, so he was crying and yelling, “Jews, O merciful Jews!”
Naturally, the more the rabbi cried, the more they laughed at him and said, “Should we feel sorry for your wife because she wants to decorate herself? What mercy is there here? With the poor man there was necessity, and this is called a ‘lack.’ We all felt the lack, so each of us felt compelled to mend it.”
From this allegory we can understand the difference between lack and decoration: a lack is when he is bear and destitute; then you can speak of mercy. But when you have a bountiful home but no jewelry, which is accessories that only a few in a generation have, you cannot speak of a lack, since they can live without it, too.
It is likewise here. The light filled the whole of the will to receive until there was no place empty, without abundance, as it is written that the upper light filled the whole of reality and there was no vacancy. This is called “He and His name are one,” when there is no discerned difference between the light and the Kli, since without a Kli, the light would not be able to expand, since the desire to do good to His creations would not be able to work without the existence of a desire to receive. Therefore, there was no distinction between the light and the Kli, as both are equally important with respect to the goal.
This brings up the question, “Why was there a Tzimtzum?” The answer to this is that the Tzimtzum was in order to decorate. This means that decorations are needed in order to improve the gift. Although now he has abundance because the light fills the whole Kli, it is still possible to make it better, meaning that the reception of the abundance will not be regarded as reception, but as bestowal, by making it reception in order to bestow, which is regarded as actual bestowal.
This is why the Tzimtzum is regarded as free choice, meaning that he had the choice to not perform a Tzimtzum, for who forced him? After all he was given and he received, and if he wanted, he could stay in that state and have abundance. However, he chose that it is better to perform a Tzimtzum and receive only in order to bestow, for by that he will be equal to the Emanator.
Only afterwards, after the Tzimtzum, it become a lack, for it is a rule that a desire in the upper one becomes a mandatory law in the lower one. Hence, the lower one no longer has a choice, meaning that even when he wants, he is not given. It follows that now, after the Tzimtzum, the will to receive is regarded as a lack because you can no longer receive anything in it, and it is discerned as darkness. Only when beginning to do things in order to bestow do we begin to equalize in form and begin to come out of the rule of the Tzimtzum. Then we begin to feel Godliness, to the extent that we can work in order to bestow.
If you have any more questions on that topic write me the places you find confusing and I will try to explain to the best of my ability. But mainly, we should hope that the Creator will give and bestow upon us the reason of the upper one so we can understand and learn to hear, to learn and to teach ourselves, to keep, do, and observe.