Hey Southcoast,
Praise God that you are in the program learning about the Catholic Church; and I truly mean that, I praise God for the work He is continuing in you. I completely understand your need for the facts, I was in your shoes not long ago. I may just be adding more words to the fray but as a means of positive reinforcement I would suggest a couple of things.
The reason that assisting at Mass on Sunday or it's vigil and on Holy Days is a mortal sin has to with it's impact on our relationship with God. As Skripper noted the commandments say, "Remember the Sabbath day by keeping it holy." Exodus 10:8. The Christian Church acknowledges Sunday for various reasons noted above by many as that Sabbath day. We as Catholics keep it holy not by just gathering to hear the Word of God, which in itself is important, but to re-present the sacrifice of our Lord as the only atonement for our daily sins.
As we conform to the Divine will (which by the way requires both obedience and surrender, tough stuff) we desire to be present as fully with Christ as we can. The call to celebrate the Lord's Supper is a call from Christ himself. He reaches out to each of us in a unique way at every Mass we attend. It is also a moment of living Heaven on Earth. Conforming to the will of God means striving to live out His will on earth as it is in Heaven. The more often we experience Heaven on Earth the less of Earth we wish to experience. I think you will find that you will desire the Mass more often once you begin to walk in the light of Eucharist. Your desire to "get away" (into the world) will be less and your desire to "get away"(from the world) will be greater. Let God do this work at His pace. He knows what is right for you.
There will be times when you are unable to attend a Mass and if through no conscience fault of your own you miss Mass you are not in Mortal sin. If you choose to not attend when you could that's a different story. I travel often for business and before I even leave my house I check out
www.masstimes.org and find a Mass in the area I am going that fits my schedule. I also love visiting different churches.
I'll be honest I've changed 180 degrees since I first returned to the Church regarding obedience. I am now quite thankful that the Church has written this "rule" down. Many times I feel tired, burned out or just not up for dealing with people and would love to skip Mass but I go, knowing that Christ is present and waiting for me in a unique way. Always I am blessed but sometimes it takes that nudge, "I don't want to have to confess this for no good reason" to push me through the door. Once when I did have to confess it I received such a beautiful direction from the Priest which I have never forgotten. He showed me how attending Mass was a visible fidelity to Our Lord. It's not just about being with others or even wanting it for ourselves and our own growth but it's about pleasing, comforting, and loving Jesus in a special way. We choose fidelity to so many people; spouses, children, friends. We would never let them down. As Jesus waits for us to be present with Him in His sacrifice we have a special opportunity to love Him with our presence.
The Mass is done throughout the world every day at various times during the day. Part of our commitment as Christians is to keep the rememberence of Christ and Him crucified. If everyone said "Well not today, I need a break from that whole church thing", it would be left only to the priests of the Church to commemorate Christ. That is far from the unity of the body of Christ that Jesus himself pleaded to the Father for.
John 17:
I pray also for those who will believe in me through their message, 21that all of them may be one, Father, just as you are in me and I am in you. May they also be in us so that the world may believe that you have sent me. 22I have given them the glory that you gave me, that they may be one as we are one: 23I in them and you in me. May they be brought to complete unity to let the world know that you sent me and have loved them even as you have loved me. 24"Father, I want those you have given me to be with me where I am, and to see my glory, the glory you have given me because you loved me before the creation of the world. 25"Righteous Father, though the world does not know you, I know you, and they know that you have sent me. 26I have made you known to them, and will continue to make you known in order that the love you have for me may be in them and that I myself may be in them."
Finally I would just add that in your search for knowledge, check out Scott Hann's book, The Lamb's Supper. I think you will really appreciate it.
Blessings to you,
Maggie