The fundamental reason that God gives for the Feast of Unleavened Bread is to remember His deliverance. He delivered Israel physically, but us spiritually.
Israel was to keep the Night to Be Much Observed as a night of watching—of watchful vigil—to commemorate the reason they were able to leave Egypt so easily.
Unleavened bread serves as a memorial of God's deliverance from the bondage of sin. We must realize that our part of the salvation process is to follow God.
We keep Unleavened Bread because of what God did to bring us out of sin (typified by Egypt). While God compels us to make choices, He is with us all the way.
Nothing happens in our lives (including repentance) until God initiates it. A change of heart, by God's Holy Spirit, results in a total change of direction.
We will not have faith tomorrow simply because we had it yesterday; we must renew faith daily by deliberately remembering God's prior interventions.
The Feast of Trumpets memorializes God's deliverance of Israel beginning with Joseph, and looks forward to Christ's return when God will deliver His people.