1. The Covenant-Basis of the Relationship. God made a covenant with Abraham, Isaac, and Jacob and with their descendants; so, Israel stood in a covenant relationship with God. (2Kgs.13:23)
2. The Continuity of the Relationship. Jesus declared that the phrase "of Abraham, of Isaac, and of Jacob" implied that God was the God of the living and not of the dead. The phrase didn't become obsolete when the three patriarchs physically died. The phrase was valid because they were alive in the spirit, and God was the God of living; which also meant that the relationship was a living and continuing one (Matt.22:32; Mark 12:25,26; Matt.8:11). God's relationship with Israel as a nation didn't die when the patriarchs died physically. It continues on.
3. The Completeness of the Relationship. God made sure to ratify His covenant with each of the fathers. It was irrevocable and complete. The line of blessing was specifically chosen. Of course, Ishmael had to go; and so, Esau. But, the identity of the children of Israel as a chosen covenant people was established completely in the line of Abraham-Isaac-Jacob.
This further revealed their
Rootedness as a nation in God, by God, of God, and for God.
Responsibility as a nation in God, by God, of God, and for God.
IN THE NEW TESTAMENT, however, with regard to the Church, the phrase "of Abraham, of Isaac, and of Jacob" is not used. Of course, Jesus did speak of people coming from various parts to sit at table with the three patriarchs when the Kingdom comes (Matt.8:11); and Peter used it with respect to the Jews (Acts 3:13); however, the possessive phrase used for the disciples of Christ is different. God is called as:
God our Father and the Lord Jesus Christ (Phil.1:2; Col.1:2; 1Thess.1:1)
God and Father of our Lord Jesus Christ (2Cor.1:3; 11:31; Eph.1:3; Col.1:3; 1Pet.1:3)
God of our Lord Jesus Christ (Eph.1:17)
From God the Father and from the Lord Jesus Christ, the Son of the Father, in truth and love (2Jn.1:3)
For sure, this relationship is a stronger Covenant Relationship (Heb.12:24), an eternally Continuing Relationship (Heb.7:16,17), and an absolutely Complete Relationship (Heb.6:18; Col.2:10). But, the phrases, noticeably have also at least two different versions. The first is:
"God and Father of our Lord Jesus Christ" (2Cor.1:3; 11:31; Eph.1:3; Col.1:3; 1Pet.1:3)
It reminds us of four things:
1. The Finality of Revelation in Christ. In the old, God spoke through the fathers; but, in the last days through His Son. (Heb.1:1,2)
2. The Fatherhood of God in Christ. God is not just the God of our fathers, but He is God and Father of our Lord Jesus Christ. Christ is called as the Son. (Of course, He is called the "Everlasting Father" in Isaiah 9:6; however, in the Triune relationship with us, He is the Firstborn). Zac Poonen has pointed out that Christ was always called as the only begotten Son before His resurrection; but, after His resurrection, He is known as the Firstborn among many brethren (Rom.8:29). We don't look back to our fathers as a second or third generation; but, we look back directly to God who Himself is our Father through our Lord Jesus Christ.
3. The Fullness of the Authority of Christ. Unlike Abraham, Isaac, and Jacob, Jesus died and rose and again and is exalted to the right hand of God and is given a Name above all names. He is our Lord. His authority in the Church and in His Kingdom is complete and final. While the Jews looked back at the patriarchs as their fathers, we look up to Jesus as our Lord.
4. The Favor of God on all humanity through Christ. It points us to our Root; the one who is called the Source and Root of Jesse (Israel) is now also the hope of all mankind (both Jews and Gentiles alike). (Isaiah 11:10; Rom.15:12). The identity of the Christian doesn't come from any race, religion, culture, or language; but, it comes from Christ alone. While the Jews could proudly talk of the God of Abraham, of Isaac, and of Jacob, the believers could only joyfully talk of the God and Father of our Lord Jesus Christ.
The other version of the phrase is:
God our Father and the Lord Jesus Christ (Phil.1:2; Col.1:2; 1Thess.1:1).
This is usually used in statements where there is a talk of proceeding from (grace and mercy from) or identity in (1Thess.1:1). The phrase also implies at least three facts:
1. The Co-Equality of the Son with the Father. The conjunction "and" places the two persons of the Divine Godhead together.
2. The Co-Substantiality of the Son with the Father. The identity of the Church in God and the Son as well as the procession of grace and mercy from God and the Son point to the unity that is within the Godhead. There are not two sources but one (Rev.22:1).
3. The Co-Eternality of the Son with the Father. The above two logically imply the understanding of the Son as co-eternal with the Father.
Therefore, Paul calls it the mystery of godliness:
Without controversy great is the mystery of godliness: God was manifested in the flesh, Justified in the Spirit, Seen by angels, Preached among the Gentiles, Believed on in the world, Received up in glory. (1Ti 3:16 NKJ)