The first thing that I learned was that the word Gospel means Good News. That changed my question from "What is the Gospel?" to "Why is the Gospel such good news?" I found the answer as I looked at the five steps of the gospel individually:
Faith: The first step in the Gospel of Jesus Christ is Faith in Him. Faith entails trusting in His words and commandments, and believing that His sacrifice and Atonement have the power to change and improve us.
Repentance: The next step in the Gospel is repenting of our sins. Repentance is only possible if we have faith in Christ's Atonement, and the act of repenting actually builds our faith! It's a self-continuing cycle. When we repent, we feel bad for transgressing God's commandments and ask Him for forgiveness. We feel the sweet peace that comes from knowing that God has forgiven us and has given us a second chance.
Baptism: The only tangible step to the Gospel of Jesus Christ is being baptized by someone holding the proper authority, what we call the Priesthood. Christ Himself demonstrated this step by walking 40+ miles to the only man with the authority to baptize at that time: John the Baptist. He taught that baptism is a symbol of our devotion to God and a promise that we will serve Him. In turn, God seals the forgiveness that we received during the repentance process and allows us to progress to the fourth step of the Gospel.
The Holy Ghost: Baptism qualifies us for the reception of the Holy Ghost or Holy Spirit. The Holy Ghost is the third member of the Godhead and is God's personal messenger to each of us. Before baptism, He can lead and guide us towards truth, but after baptism we are promised that He will remain with us ALWAYS, as long as we remain worthy by keeping the commandments. His role is to build our faith in God and Jesus Christ and to help us progress through life.
Enduring to the End: This final and crowning step is a continuous repetition of the other four. It involves building our faith by keeping the commandments and repenting when we mess up, living true to our baptismal promises, and striving to have the Holy Ghost with us always. Enduring to the End means living true to the principles that we believe now and forever, throughout our lives.
So, here we are. We have our five steps to the Gospel of Christ. As I said, we learn in the scriptures that these are EVERYTHING we need to gain Salvation (which is just a fancy word for "go to heaven"). All other things that we teach in the church are just appendages to these! The Priesthood is simply the authority necessary to perform baptism and preach the gospel. The commandments are the qualifications for and the promises made at baptism. The sacred work we do in the Temples are tools for enduring the end. Scripture study, prayer, and church attendance build our faith and help us keep the Holy Ghost with us always. Everything points to the Good News.
The Good News of the Gospel is this: because Jesus Christ loved us enough to come down here, live a perfect life, suffer for our sins, and then give up his life for us, we are not doomed to fail. Through Christ's Atonement, we can be forgiven of our sins, we can overcome our weaknesses and addictions, and we can become more Christlike each and every day!
I know that the Gospel truly is God's plan for each one of His children, because I have seen and felt it work in my life every day! There have been many times in my life when I've had cause to doubt the things I believe and give up, but The Lord has been there to help me endure, and I know He'll help me to the end. I have felt the sweet peace and comfort that comes from the Holy Ghost, and I have felt it testify to me that Jesus truly is the Christ. As I've grown to better understand the promises I made when I was baptized, I've learned to appreciate and honor that sacred ordinance. Every day I strive to repent of my sins and thus come closer to my Savior. And above all, I have felt the sustaining power and peace that come from faith in Christ and His Atonement.
I have seen the Good News work miracles in the lives of the people I have taught, and I KNOW that these are the things that qualify each of us to live again in God's presence. I feel so privileged to be a missionary, sharing these things that I have learned.