Salvation history, properly so-called, begins with Abram, whom God named Abraham which means "father of a multitude." Abraham was the first patriarch of the people of Israel. The word patriarch means "the father of the people." In the person and life of Abraham, the central events of the salvation of the world by Christ in the New Testament have been prefigured.
God made the first promise of His salvation of all the people of the earth to Abraham, with whom He also made His covenant to be faithful forever.
Now the Lord said to Abram, "Go from your country and kindred and your father's house to the land that I will show you. And I will make you a great nation, and make your name great, so that you will be a blessing … and in you all families of the earth shall be blessed" (Gen 12:1-3, See also 17:1-8, 22:1-18).The fulfillment of the promise to Abraham comes in Jesus Christ. He is the descendant of Israel's first father in whom all the families of the earth are blessed. Thus, Mary, the Mother of Jesus, sings at her time of waiting for the Savior's birth, that all generations will call her blessed because the fulfillment has come from God "as He spoke to our fathers, to Abraham and to his posterity forever" (Lk 1:55, see also Zachariah's Song in Lk 1:67-79). All through the New Testament the claim is made that God's promise to Abraham is fulfilled in Jesus.
Now the promises were made to Abraham and to his offspring. It does not say, "And to off springs," referring to many; but, referring to one, "And to your offspring," which is Christ (Gal 3:16).The faith of Abraham is prototypical of al those who in Christ are saved by faith. The New Testament stresses faith as necessary for salvation. The model for this faith is Abraham.
Abraham believed God, and it was reckoned to him as righteousness (Gen 15:6, Rom 4:3).Abraham's faith was united to his works, and was expressed in his works.
Was not Abraham our father justified by works, when he offered his son Isaac upon the altar? You see that faith was active along with his works, and faith was completed by works, and the scripture was fulfilled which says, "Abraham believed God, and it was reckoned to him as righteousness;" and he was called the friend of God. You see that a man is justified by works and not by faith alone (Jas 2:21-24).God tested Abraham by commanding him to sacrifice his beloved son Isaac as a burnt offering. Abraham believed and trusted in God. He obeyed his will, and went to the mountain to slay his child. God stopped him and placed a ram in Isaac's place saying "for now I know that you fear God, seeing that you have not withheld your son, your only son, from me" (Gen 22:12). Then once more God made the promise that "by your descendants shall all of the nations of the earth be blessed …" (Gen 22:18).
The sacrifice of Isaac is not only a testimony to Abraham's faith. It is also the original sign that God Himself does what He does not allow the first and foremost of His People to do. No ram is put in the place of God's Son, His only Son Jesus, when He is sacrificed on the cross for the sins of the world.
The perfect priesthood of Christ is also prefigured in Abraham's life. It is the priesthood of Melchizedek, the King of Peace. It is the priesthood in which the offering is bread and wine. It is the priesthood which is before that of the Levites, and the one which is that of the Messiah, Who is "a priest forever according to the order of Melchizedek" (Ps 110:4, Heb 5-10).
So also Christ did not exalt Himself to be made a high priest, but was appointed by Him Who said to Him, "Thou art my Son, today I have begotten thee;"as He says also in another place, "Thou art a priest for ever, after the order of Melchizedek."The most sublime of the New Testament revelations, that of the Holy Trinity, was also prefigured in Abraham's life. This is the famous visit of the three angels of God to Abraham under the oaks of Mamre.
In the days of His flesh, Jesus offered up prayers and supplications, with loud cries and tears, to Him Who was able to save Him from death, and He was heard for His godly fear. Although He was a Son, He learned obedience through what He suffered; and being made perfect He became the source of eternal salvation to all who obey Him, being designated by God a high priest after the order of Melchizedek (Heb 5:5-10).
For this Melchizedek, king of Salem, priest of the Most High God, met Abraham returning from the slaughter of the kings and blessed him; and to him Abraham apportioned a tenth part of everything. He is first, by translation of his name, king of righteousness, and then he is also king of Salem, that is king of peace. He is without father or mother or genealogy, and has neither beginning of days nor end of life, but resembling the Son of God he continues a priest for ever (Heb 7:1-3).
And the Lord appeared to him by the oaks of Mamre, as he sat at the door of his tent in the heat of the day. He lifted up his eyes and looked, and behold, three men stood in front of him. When he saw them, he ran from the tent door to meet them, and bowed himself to the earth, and said, "My lord, if I have found favor in your sight, do not pass by your servant. Let a little water be brought, and wash your feet, and rest yourselves under the tree, while I fetch a morsel of bread, that you may refresh yourselves, and after that you may pass on … since you have come to your servant." So they said, "Do as you have said" (Gen 18:1-5).Abraham addresses the three angels as one, calling them Lord. They eat in his presence and foretell the birth of Isaac from Sarah in her old age. In this visitation of God to Abraham, the Orthodox Church sees the prefiguration of the full revelation of the Holy Trinity in the New Testament.
Because there can be no depiction of God the Father and the Holy Spirit in human form, Orthodox iconography has traditionally painted the Holy Trinity in the form of the three angels who came to Abraham. The most famous icon of the Holy Trinity, the one often used in the Church on the feast of Pentecost, is that of Saint Andrew Rublev, a disciple of Saint Sergius of Radonezh in Russia in the fourteenth century.
Thus the salvation of the world which has come in Christ was prefigured in the life of Abraham, as well as the Christian doctrine about faith and works and the Christian revelations about the sacrifice, the priesthood, and even the most Holy Trinity. Truly in Abraham every aspect of the final covenant in Christ the Messiah was foreshadowed and foretold.
From:The Orthodox Faith by Fr. Thomas Hopko