The book of Exodus (meaning, "going out", or "the way out") is one of the richest in terms of new information as well as in its purpose of illustrating how God's graces are bestowed upon the Israelites; a race described as "the chosen one". Hence, depending upon what is important to the reader, we could argue that the information which is most salient from Exodus is a) the confirmation of who is God, b) the ten commandments, and c) the various ways in which God's devotion to His people is illustrated through miracles.
The main thing that the book of Exodus reveals all over is the affirmation to the Israelites of who is God, and the revelation of His name to Moses
I AM WHO I AM (3:14)
Of equal importance is the knowledge that the God of Moses is the same as the God of Abraham and his descendants. Hence, this gives confirmation to the Israelites of their unique position under the grace of a God that is willing to do anything for them.
And the LORD said unto Moses, put forth thine hand, and take it by the tail. And he put forth his hand, and caught it, and it became a rod in his hand: that they may believe that the LORD God of their fathers, the God of Abraham, the God of Isaac, and the God of Jacob, hath appeared unto thee. (4:5)
The second most important thing that we can get from Exodus is found in 20:1-17, which is the moment when God gives Moses the Ten Commandments. The commandments, which are still part of the backbone of the Christian faith, focus on building a relationship with God as well as with the rest of mankind.
Perhaps to anyone in the faith, however, the most important thing in Exodus is the clear and obvious devotion that God places upon the people of Israel. Not only does he literally part the Red Sea to allow their crossing from Egypt toward their new land (found in 13:14-12:29), but he also provides them with the unique food of manna during the trying times in the desert (16:4-5). These are unique actions from a quite-unique entity which is determined to protect and defend those that are thought to be "His" people. The extent to which these actions affect the history of the Israelites is certainly quite profound.
Therefore, out of several important things that can be found in Exodus, it is arguable that some of the most important ones include a) the learning of God's identity, b) the giving of the Ten Commandments and, c) the illustration of how much God is willing to do for the people of Israel, from parting the sea, to creating their sustenance in the desert.