So we have to become Jews first, before we can be Christian? That sounds oddly familiar...
Not at all there are only BELIEVERS and UNBELIEVERS in God's Israel, because it is written....
Romans 2
28, For he is not a Jew, which is one outwardly; neither is that circumcision, which is outward in the flesh:
29, But he is a Jew, which is one inwardly; and circumcision is that of the heart, in the spirit, and not in the letter; whose praise is not of men, but of God.
Rom 10:12
For there is no difference between the Jew and the Greek: for the same Lord over all is rich unto all that call upon him.
Gal 3:28
There is neither Jew nor Greek, there is neither bond nor free, there is neither male nor female: for ye are all one in Christ Jesus.
Col 3:11
Where there is neither Greek nor Jew, circumcision nor uncircumcision, Barbarian, Scythian, bond nor free: but Christ is all, and in all.
Romans 9
6, Not as though the word of God hath taken none effect. For they are not all Israel, which are of Israel:
7, Neither, because they are the seed of Abraham, are they all children: but, In Isaac shall thy seed be called.
8, That is, They which are the children of the flesh, these are not the children of God: but the children of the promise are counted for the seed.
9, For this is the word of promise, At this time will I come, and Sara shall have a son.
God's Israel are those that BELIEVE and FOLLOW the WORD of GOD. Those that do not BELIEVE and FOLLOW the Word of God are the UNBELIEVERS. It is the UNBELIEVERS in God's Word that have no part in the Kingdom of Heaven because they are still in their SINS because they have rejected the gift of God's dear son. (Hebrews 10:26-27; Romans 6:23)
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God's 4th commandment is one of the ten (Exodus 20:8-11) and like any of the ten, if we knowingly break it when God asks us not to we stand guilty before God of committing sin (James 2:8-12). If we do not seek him in repentance and forgiveness we are in danger of the Judgement (Hebrews 10:26-27)
There is not one scripture in ALL of God's WORD that says God's 4th commandment is now ABOLISHED and we are now commanded to worship God on Sunday in it's place.
Sunday worship is a tradition and teaching of man that has lead many to break the commandments of God. Jesus says that if we follow the traditions of man that break the commandments of God we are not following God (Matthew 15:3-9)
Who should we follow the teachings and traditions of men or the Word of God? Who should we believe the Words of men or the Word of God?