i am going to just copy and paste some things i wrote in another thread several months ago...because i think i did a good job of writing it then...
the biggest difficulty that usually comes up right away in discussions of this topic is misunderstanding about what 'replacement theology' actually is...many people assume that anything that isn't dispensationalism must be some form of replacement theology...when really in the scriptural alternative to dispensationalism nothing is actually 'replaced' at all!
the main issue here is understanding what the biblical definition of 'israel' is...here are some scriptures that make it clear...
exodus 12:48..."But if a stranger sojourns with you, and celebrates the Passover to the Lord, let all his males be circumcised, and then let him come near to celebrate it; and he shall be like a native of the land. But no uncircumcised person may eat of it."
this verse indicates that anyone could join the israelite community and gain all of the 'native born' rights of an israelite...such as the right to celebrate the israelite feasts...by becoming circumcised...that is by entering into the covenant between God and israel...
we are familiar with God's prohibition against israelites intermarrying with people from the surrounding nations...
deuteronomy 23:3-4..."No Ammonite or Moabite shall enter the assembly of the Lord; none of their descendants, even to the tenth generation, shall ever enter the assembly of the Lord, because they did not meet you with food and water on the way when you came out of Egypt, and because they hired against you Balaam the son of Beor from Pethor of Mesopotamia, to curse you."
similarly there was a prohibition against israelites marrying the people who were already living in the land before their arrival...
deuteronomy 7:3-4..."Furthermore, you shall not intermarry with them; you shall not give your daughters to their sons, nor shall you take their daughters for your sons."
however we know of cases where israelites -did- intermarry with moabites and canaanites...and in fact there are moabite and canaanite women in the lineage of the messiah...namely...
ruth 4:13..."So Boaz took Ruth, and she became his wife, and he went in to her. And the Lord enabled her to conceive, and she gave birth to a son."
matthew 1:5..."Salmon was the father of Boaz by Rahab, Boaz was the father of Obed by Ruth, and Obed the father of Jesse."
so why were these two women exceptions to the rule against intermarriage with gentiles? the answer is in these passages...
joshua 2:11..."When we heard it, our hearts melted and no courage remained in any man any longer because of you; for the Lord your God, He is God in heaven above and on earth beneath."
ruth 1:16-17..."But Ruth said, 'Do not urge me to leave you or turn back from following you; for where you go, I will go, and where you lodge, I will lodge. Your people shall be my people, and your God, my God. Where you die, I will die, and there I will be buried. Thus may the Lord do to me, and worse, if anything but death parts you and me.'"
especially compare rahab's confession of faith with the words of moses to the israelites...
deuteronomy 4:39..."Know therefore today, and take it to your heart, that the Lord, He is God in heaven above and on the earth below; there is no other."
so a gentile could become part of the israelite community and enter into the covenant through faith in the God of israel...
conversely it was possible for an ethnic israelite to be -excluded- from the israelite community and from the covenant for acts demonstrating -unfaithfulness- to the God of israel...for example...
genesis 17:14..."But an uncircumcised male who is not circumcised in the flesh of his foreskin, that person shall be cut off from his people; he has broken My covenant."
leviticus 18:29..."For whoever does any of these abominations, those persons who do so shall be cut off from among their people."
the apparent fact that comes out of scripture is that israel was never an -ethnic- community at all...nobody was excluded from israel merely on the basis of gentile ethnicity...and likewise nobody was entitled to inclusion in israel solely because of abrahamic ancestry...
instead israel even in the old testament was a -faith- community...a community made up of everyone...whether abrahamic or gentile...who put their faith in the God of israel and chose to bind themselves in covenant to israel's God...
the new testament emphasizes this truth even more strongly...for instance...
ephesians 2:19-22..."So then you are no longer strangers and aliens, but you are fellow citizens with the saints, and are of God’s household, having been built on the foundation of the apostles and prophets, Christ Jesus Himself being the corner stone, in whom the whole building, being fitted together, is growing into a holy temple in the Lord, in whom you also are being built together into a dwelling of God in the Spirit."
so the church did not 'replace' israel...instead God's israel and God's church are the -same thing-...the church has always been israel and israel has always been church...
even the greek word for 'church'...ekklesia...means an assembly called out...compare that with references to 'the assembly' in the old testament scriptures referring to israel...such as deuteronomy 23:3-4 that i quoted above...
the organic unity of israel and the church is a direct implication of this verse...
ephesians 4:4-5..."There is one body and one Spirit, just as also you were called in one hope of your calling; one Lord, one faith, one baptism, one God and Father of all who is over all and through all and in all."
if there is only one body and one faith...then israel and the church cannot be two separate bodies treated differently by God as in dispensationalism...nor can they be two separate bodies such that one replaces the other in God's plan as in the -real- replacement theology that actually is taught by some...
israel and the church have always been one faith community...always encompassing both genetic descendants of abraham and also gentiles in unity of faith in God and christ...and they are the sole 'people' with whom God's plan of salvation is concerned...
so the biblical truth is not 'dispensational' theology or 'replacement' theology...the biblical truth is -unity- theology!
i also posted this...
here is one more scripture passage that clearly demonstrates what i am saying...it comes just a little bit before one of the verses i quoted in my previous post but i forgot to include it...
ephesians 2:11-16..."Therefore remember that formerly you, the Gentiles in the flesh, who are called 'Uncircumcision' by the so-called 'Circumcision,' which is performed in the flesh by human hands—remember that you were at that time separate from Christ, excluded from the commonwealth of Israel, and strangers to the covenants of promise, having no hope and without God in the world. But now in Christ Jesus you who formerly were far off have been brought near by the blood of Christ. For He Himself is our peace, who made both groups into one and broke down the barrier of the dividing wall, by abolishing in His flesh the enmity, which is the Law of commandments contained in ordinances, so that in Himself He might make the two into one new man, thus establishing peace, and might reconcile them both in one body to God through the cross, by it having put to death the enmity."