There's much more that matters for belief, but that's the core - the miracle of God's Birth as man, His life on Earth, His death and resurection, are the major features that a believer must be able to accept. Without that, there is no salvation, no grace, no forgiveness, no redemption.
Once we master this, however, what more is there we need to understand? Isn't that all that's important? That sums up the entire requirements for salvation and eternal life, doesn't it?
Not by a long shot.
We must learn the message of Genesis, that God created the heavens and the earth, and all things that exist are His creations. Quibbling on whether it happened literally in six days (when God didn't separate Light from dark and call the light "day" until day Four...) or otherwise is foolishness - trying to decide which came first, the chicken or the egg. The truth of God's creation is more important than the quibble over timelines.
We must also learn the wisdom handed down from us by God's chosen people, the Jews, who were selected from all others to bear the Word of God to all men. The Old Testament is filled with successes and failures, of rewards and punishments, and God's steadfastness in guiding and teaching His chosen people. We need to learn the lessons, both of faith and failure, that are shown there for us, so that we don't make the same mistakes.
The words of the New Testament show us not only a glimpse of the life of Jesus, but also how his followers accepted and reacted to His death and resurection, and the Gift of the Holy Spirit. We're given ample examples of what God expects of us in spreading His Word, and in granting His salvation.
Nor has God stopped talking to us. He has promised to be "with us always, even unto the ends of the Earth". He has promised to guide and direct us, so that we may not stray from His path. He has also warned us of false prophets, and of those who will preach in His name, but not for His good.
One of the problems many people today have with God is that He demands we adhere to His teachings completely. We can't be "10%
Christians" - doing what we wish six days of the week, then attend Church on the Sabbath and believe we're doing the will of God. What's true on the Sabbath is true also the other six days of the week, or else our beliefs are weak and we're not true to God.
Another failure of the people to understand God's will is the complaint that "God's laws are so old fashioned, He needs to get with it". Times, indeed, have changed - but times ALWAYS change. God gave us ten Commandments that were immutable. He gave the Jews laws that were both to bind them to God, and to keep them separate from other tribes and nations, for God's purpose. Their success today, their ability to survive where others were destroyed, is both a testament to their faith and to God's promise to them.
Many of the laws God gave to the Jews apply to us who are Christian, just as they do to Jews and Hebrews. There are some things God commands us are abominations, not to be tolerated. There are others which are sins, that can be forgiven, but only with due pentence and repudiation. Denying that God's laws apply today just as they did ten thousand years ago is to deny God, who is, and was, and always will be. We all have vices, we all do things which God has commanded us not to do, but some people have a harder time asking for forgiveness, have a difficult time repenting their sins, and "go, and sin no more", as Jesus said to Mary Magdaline. Yet that's exactly what God demands of each of us.
The Catholic Church has just selected a new Pope, following the death of Pope John Paul II. Both the new Pope, Benedict XVI and Pope John Paul II reaffirmed the long-held fundamental practices of the Catholic Church, again confirming that some behaviors were "incompatible with Church teachings and the beliefs and traditions of the Church". I'm not a Catholic, but I appreciate the dedication of those who hold fast to what's fundamentally right, regardless of those that rail against it. Holding fast is a sign of strong faith, not the "bone-headed stubbornness" those that wish to weaken the Church label it. Let us all hope that we can be equally "bone-headed stubborn" about the truth of God's love for us, and His rules that we uphold in order to show our faith.