Mastery of the Holy Bible can be very difficult to achieve. It takes prayer, study, and constant reading and re-reading - not to mention an intimate familiarity the teachings of the Church Fathers. However, one can quickly acquire an "outline" of salvation by history by learning the basic covenants of Scripture. The covenants provide the structure for the unfolding of God's plan. Ultimately all things are fulfilled in Christ in the New Covenant. Here is how it works:
- Adamic Covenant: God created Adam and Eve as his children and as masters of his creation. He gave them marriage and the Sabbath of signs of His love. Unfortunately, this covenant was transgress through original sin and so God promised to them the "Seed" (i.e. a divine child, Christ) of the "Woman" (i.e. Mary) that would destroy Satan (see Genesis 3:15).
- Noahic Covenant: As sin increased on earth, God focused his covenant with humanity by choosing the family of Noah. He destroyed the earth with water and gave the rainbow as a promise of his Divine Mercy. The promised "Seed" will come through the descendants of Noah.
- Abrahamic Covenant: God again focuses on the "Seed" who shall be a Savior and promises that it will come through the genetic line of Abraham. The covenant is not "sealed" on the procreative member of Abraham since the "Seed" comes from this body part. This is the promise of circumcision. All of Abraham's descendants bear this mark in expectation of the coming "Seed" promised to Adam and Eve.
- Mosaic Covenant: God reorganizes the descendants of Abraham through Moses. The idolatry of the Israelite reveals that their hearts are prone to sin and infidelity. So God establishes the Law of Moses as a way of preventing Israel from sin. It also prepares Israel for the coming birth of the Messiah - the Seed who shall save them.
- Davidic Covenant: God then establishes the people of Israel as a royal kingdom with King David as its righteous monarch. David's conquests and the expansion of Israel under his son Solomon reveal that the Salvation of humanity is not reserved for Israel alone, but for all mankind. The Psalm of David and the Proverbs of Solomon indicate a universal application of God's law to all men.
- New Covenant: At last, Christ the Seed of the Woman is born in Bethelehem. He fulfills the Adamic Covenant by being the "New Adam" by being without original sin and the true Son of God by His nature. His fulfills the promise of Noah, but establishing the sacrament of baptism, which fulfills the universal flood which removed sin from the world. He fulfills the Abrahamic Covenant because he is a genetic heir of Abraham and he receives circumcision as an infant. He fulfills the Mosaic Covenant because He obeys and fulfills all the precepts of Moses as a dutiful Jew. His death on the cross is the liturgical, sacrificial, and sacramental fulfillment of the Jewish Passover and all the blood sacrifices of the Old Law. This is why He said: "This is the blood of the new and everlasting covenant." It is the Eucharist that ratifies the New Covenant and fulfills all that came before.
I hope that's not too long. If you memorize this structure than reading the Bible will make more sense. The covenants are like mile markers along the journey. They help you know where you are and how long you have to go.
PS: Much more could be said (e.g. of Abraham's sacrifice of Isaac) but this is meant to be a brief introduction.