God made the calling for the First Covenant to Noah, just after the Great Flood: that was the moment when “a new mankind” emerged.

“God said to Noah and to his sons with him: ‘See, I am establishing my covenant with you and your descendants after you and with every living creature that was with you’” (Genesis 9,8-10). God chose the rainbow as the sign of this Covenant (Genesis 9, 12-17).

Afterwards God called Abraham to be the Father of His People, and that fact would have repercussions over the whole of mankind in the future reality of the Church.

“I will make of you a great nation, and I will bless you; I will make your name great, so that you will be a blessing” (Genesis 12, 2). “Look up at the sky and count the stars, if you can. Just so, he added, shall your descendants be. Abraham put his faith in the Lord, who credited it to him as an act of righteousness” (Genesis 15, 5-6).

“I am God the Almighty. Walk in my presence and be blameless. Between you and me I will establish my covenant, and I will multiply you exceedingly” (Genesis 17, 1-2).

Abraham celebrated the Covenant through the visible sign of circumcision: “Thus my covenant will be in your flesh as an everlasting pact” (Genesis 17, 10-13).

When the “fullness of time” had come, that Covenant would be celebrated in a definite eternal way: the Immolated Lamb.
The Lord will re-affirm that same Covenant in Isaac, Sarah’s son:
“Nevertheless, your wife Sarah is to bear you a son, and you shall call him Isaac. I will maintain my covenant with him as an everlasting pact, to be his God and the God of his descendants after him. As for Ishmael, I am heeding you: I hereby bless him, I will make him fertile and I will multiply him exceedingly. He shall become the father of twelve chieftains, and I will make of him a great nation. But my covenant I will maintain with Isaac, whom Sarah shall bear to you by this time next year” (Genesis 17, 19-21).
God also renews His Covenant with Jacob, renamed as Israel and from whom the Twelve Tribes of Israel will be born and settle in the “Promised Land” (Genesis 12, 1-7; 15, 18).

“I, the Lord, am the God of your forefather Abraham and the God of Isaac; the land on which you are lying I will give to you and your descendants. These shall be as plentiful as the dust of the earth, and through them you shall spread out east and west, north and south. In you and your descendants all the nations of the earth shall find blessing” (Genesis 28, 13-14).
The historical preparation of the Church goes on when God chooses Israel to be His People. This Covenant is made on Mount Sinai:
“Therefore, if you hearken to my voice and keep my covenant, you shall be my special possession, dearer to me than all other people, though all earth is mine. You shall be to me a kingdom of priests, a holy nation” (Exodus 19, 5-6).

The Twelve Tribes of Israel represent God’s People during the Old Covenant.

During their pilgrimage in the desert, Israel is already called “God’s Church”. Nehemiah mentions the “assembly of God” in his Book in the Gospel (Nehemiah 13,1).