Speak ye unto all the congregation of Israel, saying, In the tenth day of this month they shall take to them every man a lamb, according to the house of their fathers, a lamb for an house... Your lamb shall be without blemish, a male of the first year... and the whole assembly of the congregation of Israel shall kill it in the evening... And they shall take of the blood, and strike it on the two side posts and on the upper door post of the houses, wherein they shall eat it. And they shall eat the flesh in that night, roast with fire, and unleavened bread; and with bitter herbs they shall eat it... And thus shall ye eat it; with your loins girded, your shoes on your feet, and your staff in your hand; and ye shall eat it in haste: it is the Lord’s passover.
And then in verse 11,
And thus shall ye eat it; with your loins girded, your shoes on your feet, and your staff in your hand; and ye shall eat it in haste: it is the Lord’s passover... (why?) For I will pass through the land of Egypt this night, and will smite all the firstborn in the land of Egypt, both man and beast; and against all the gods of Egypt I will execute judgment: I am the Lord... And the blood shall be to you for a token upon the houses where ye are: and when I see the blood, I will pass over you, and the plague shall not be upon you to destroy you, when I smite the land of Egypt.
So, why the unleavened bread and why eat the lamb with their loins girded, shoes on their feet, and staff in their hands?
First, when you make bread, you need to let it rise before you eat it. However, without leaven or yeast, the bread won't rise. Letting the bread rise takes time. The Israelites did not have time to properly eat a meal or let the bread rise (using yeast or leven) because they needed to flee from the Egyptians. Second, get thee out of that land!
The Israelites had their "loins girded, [their] shoes on [their] feet, and [their] staff in [their] hand" so that they could flee from the Egyptians! And so, the jews would prepare for the passover in the same manner, ready to symbollically flee and the bread not raised.
The Mosaic law was a termperal law that provided temperal blessings, but it was fulfilled in Jesus Christ. The Mosaic law pointed the way to its fulfilling in the life, teachings, and sacrifice of He who gave the law. Abinanadi, in the Book of Mormon, asks, "Doth Salvation come by the Law of Moses?" He answers them by saying that he knows that if you keep all of the commandments, that you will be saved, but that "were it not for the atonement, which God himself shall make for the sins and iniquities of his people, that they must unavoidably perish notwirthstanding the law of Moses
The Law of the Gospel of Jesus Christ is the fulfillment of the Law of Moses. Whereas, the Mosaic Law pointed a way forward to the Atonement of Jesus Christ (where Jesus Christ's suffering in the Garden of Getsemane and His sacrificing of His life on Calvary's Cross grant unto the willing followers of His Gospel an immortal body, the enabling power that comes from His infiniate and eternal Atonement, and forgiveness of sins and the possibility of living eternally with Him, and with His Father, and all those who are sealed to us through the priesthood powers activated through covenants made in His Holy Temples.
2 Nephi 31:19 And now, my beloved brethren, after ye have gotten into this strait and narrow path, I would ask if all is done? Behold, I say unto you, Nay; for ye have not come thus far save it were by the word of Christ with unshaken faith in him, relying wholly upon the merits of him who is mighty to save. 20 Wherefore, ye must press forward with a steadfastness in Christ, having a perfect brightness of hope, and a love of God and of all men. Wherefore, if ye shall press forward, feasting upon the word of Christ, and endure to the end, behold, thus saith the Father: Ye shall have eternal life. 21 And now, behold, my beloved brethren, this is the way; and there is none other way nor name given under heaven whereby man can be saved in the kingdom of God. And now, behold, this is the doctrine of Christ, and the only and true doctrine of the Father, and of the Son, and of the Holy Ghost, which is one God, without end. Amen.
In Luke, chapter 22, verse 1, we read that “Now the feast of unleavened bread drew nigh, which is called the Passover” and He commanded His apostles to go and ask a man if he had a room readied for He and His disciples. “And he said unto them, With desire I have desired to eat this passover with you before I suffer. For I say unto you, I will not any more eat thereof, until it be fulfilled in the kingdom of God. And he took the cup, and gave thanks, and said, Take this, and divide it among yourselves: For I say unto you, I will not drink of the fruit of the vine, until the kingdom of God shall come. And he took bread, and gave thanks, and brake it, and gave unto them, saying, This is my body which is given for you: this do in remembrance of me. Likewise also the cup after supper, saying, This cup is the new testament in my blood, which is shed for you.
JPS

