Why is there approximately a 4 minute time constrain in which we have to eat the Matzo on the night of the Seder?
In other words what is the Halachic and spiritual reasoning behind why we must eat it at this speed?
The Talmud (Pesachim 114b) tells us that if you eat half of an olive's worth of Matza and then eat another half of an olive's worth of Matza you have fulfilled the obligation (to eat an olive's worth) provided you didn't wait too long in between. (Indeed it's quite reasonable that two bites need to be somewhat near each other in order to combine.) How long is too long? The time it takes to eat a half loaf of bread (Machloket if that is 3 or 4 eggs' worth) at a comfortable pace. Shulchan Arukh (OC 475:6) rules this way as well. (That's the same time limit for other things, like combining gulps of food on Yom Kippur (OC 612).)
In other words, you have to eat one olive's worth of bread in the time it takes someone to eat something like 6-60 olives' worths (depending how we handle the conversion). Not too bad.
(Estimates by various Poskim on the time it takes to eat a half loaf of bread range around 2-9 minutes. This is a biblical Mitzva, so best not to wait too long.)
I'll just note that a significant number of later authorities have understood the above discussion to be only Bedieved, but Lechatchila one should eat the full olive's worth of Matza at once. (Here's a Shiur on that.)