The earliset Church was essentially made up of faithful Jews who believed that Christ was the Promised Anointed One (Messiah). They went to the Sabbath (Saturday) services, and began meeting on Sunday to “break bread” ( the Eucharist) as Sunday was the day the Lord was risen.
One of the 10 Commandments (not 10 Suggestions), was that we were to keep holy the Sabbath, which the earliest Christians did.
Some time between the founding of the Church (Pentacost) and probably about 70 AD, when Rome laid waste to Jerusalem, problems arose between those Jews who accepted Christ as the Messiah, and those who didn’t, and essentially the believers were kicked out of the Jewish services. The services, which consisted of prayers and reading of what we now call Old Testament books was moved to Sunday to go along with the Eucharistic celebration.
There have been a number of reasons put forth as to how we shifted to Sunday: the Lord’s day (His Ressurection); a new “Sabbath” (as a break clean from the Jewish tradition and services to Christian tradition and services); the power that Christ gave to bind and loose as the power to set another day to worship God, apart from the Sabbath.
So, in answering your question, you need to go back to pre Christian times to understand how the Jews (from whom Christians came) viewed keeping the Sabbath. It was one of the most important commands God had given them. In fact, the OT tells us that the command to non Jews who lived among the Jews and believed in one God were to keep the covenant (loosely, the various laws the ews had to follow), and the Sabbath; it was the only law which was specifically set out.
God, who is all holy and all good, and upon whom man is completely dependent (read the Psalms for some wonderful statements as to that) is deserving of all our love; and part of that love is setting aside one day to worship Him. In fact, Christ spoke of the two Great Commandments, and the first is to Love God with your whole heart; and doing that includes keeping his laws, among which the most improtant was keeping the Sabbath.
So, missing Mass, which is our way of “keeping Sabbath”, is a viloation of one of the most important and fundamental laws of God. It is not just that the Church says so, it is because God says so. And missin Mass deliberately is deliberately violating one of God’s most fundamental laws to us.
As an aside, Missing Mass should not be viewed as something that will “cause you to go to hell”, as that tends toward a disconnected view of the issues, as if it were something outside yourself. Hell is the absence of God; choosing to miss Mass is choosing to put God in at lest second place, if not in no place at all. It is choosing the absence of God, which is hell. It is choosing hell.
The whole of the moral order and the moral rules isn’t some game, and if we mess up on a rule God plays “Gotch!”
It is about relationship with God, first, and one another second (which is how we usually work out and express our relationship with God). Choosing to not go to Mass is at its base and essence, choosing about our relationship with God.