Let us learn a posuk with Rashi

Two psukim teach us something about the process, which is called the "Exodus from Egypt". The ten plagues, which didn't change Pharaoh's position and led to the freeing of the people against his will, and against the will of his people For some reason Hashem insisted that Moshe make a new pilgrimage to Pharaoh and demand the freedom of the people before each new plague. This interchange with Pharaoh is not always the same, but it is not obvious what its purpose might be. 

Let us look back first at the promise that Hashem made to Avraham, when the first covenant was established.

Breishit chapter 15 verse 13-14"And he said to Avram. Know that your descendents shall be visitors in a foreign land, they will be enslaved, and they will oppress them for four hundred years."

"I shall judge the nation that enslaves them, and afterward they shall leave with great possessions".

Rashi comments. They will leave "with great wealth", and this was the case as it says (Shmot 12:36). Rashi is careful to point out that the prophecy (or directive from heaven) was actually the result of the Exodus process. However, Rashi doesn't explain how this is relevant to that process. Whatever the people were supposed to learn from the miracles and the leadership of Moshe, what difference does it make if they left with great wealth to go into the desert or not?

Further clarification comes in the psukim in our parsha.

Chapter 11:2 "speak to the people…..Each person shall request of his fellow, and each woman the same, silver and gold vessels. 

Rashi explains the reason for this directive to Moshe. "so that Avraham the righteous should not say that G-d fulfilled the decree to enslave them and to afflict them but did not fulfill the third part that they will leave with great possessions".

According to Rashi, the promise having been made should be kept. But it doesn't seem that there is any particular importance to the promise being kept in the grander sense. We are still in the dark about the reason for the riches.

The next verse (verse 3) has two parts. First, "Hashem granted the people favor in the eyes of Egypt". 

This means that it was not difficult to get the Egyptians to part with their property. These were not the spoils of war but an Egyptian gift to the people beginning their journey. This is further reiterated in verse 12:36. 

"Hashem granted the people favor in the eyes of the Egyptians, and they lent them (everything?) – so they emptied Egypt. Rashi adds: "They lent them "even those things which they did not ask of the Egyptians. An Egyptian would say: you say that you want one (of these)….take two and go!"

The Egyptians were not being oppressed. They gave of their own free will. They gave more than asked for. This is the special quality of chen that the verse refers to.

One more point. In verse 3 above there is a second part: "Moshe was very great in the land of Egypt, both in the eyes of Pharaoh's servants and in the eyes of the people".

Imagine, Moshe like Yosef before him has become the great man in the land. Since Moshe can give them what they need, not food this time, but peace and time to rebuild they are prepared to give Moshe and his people all that they ask for. The chen mentioned can be compared to the chen of Noach. The word describes a quality upon which the future of existence depends. Only Noach would be able to live through the flood. Only the people in Egypt would be worthy of receiving the Torah and make creation viable once again. It was important that the Egyptians recognize this, in order to end their punishment. Even those who are not receiving the Torah have to recognize that the world would not continue to exist without it.