“And on this night, they shall eat the flesh, roasted over the fire, and matzos; with bitter herbs they shall eat it.” (12:8)
Why does this verse separate the matzah from the maror, while in parshas B’haalosecha the verse joins them: “on matzos and maror they will eat it.” (Bamidbar 9:11)
There is a basic principle often mentioned by the sefer Zera Shimshon. If the Jews would have stayed in Mitzrayim the prescribed time of 400 years, and not left after only 210, there would be no need for more exiles. It would not be possible for any nation to overwhelm and subjugate them.
However, they had reached the 49th level of impurity and needed to be redeemed with haste. Therefore future exiles are necessary to complete this process.
But when they reached Har Sinai and received the luchos, they also received a reprieve from the malach hamaves and from the subjugation of the nations. Receiving the Torah freed them from any further exiles. But it was short lived. The sin of the golden calf brought them back to their original state, requiring exile to complete the missing time in Mitzrayim. The intensity of the slavery could not make their 210 years be reckoned for a full 400 years.
But can’t their misstep by the golden calf be excused because of their ex-slave state? No. Because when they worshipped the golden calf they were not under the duress of slavery. This revealed that even the idolatry of Mitzrayim was acceptable to them.
If so, it is possible that the command to eat matzah was different before the golden calf than after the sin. While still in Mitzrayim Hashem told Moshe to eat matzah as a sign of redemption, and you may not need other exiles because the intensity of the slavery made up for the missing years. Therefore the maror was separated from the matzah. But in B’haalosecha, after the sin and the requirement for further exile, the Torah puts matzah and maror together. They left Mitzrayim in haste because of their state of impurity, and the fact that it was imbedded in them was reinforced by the golden calf. After the sin, the “matzah of haste” and the bitterness of the future exiles go together.