Hey Danoh do you think that if a believing Israelite, such as the ones to whom James and Peter wrote their epistles, and Jude---if one of them did Romans 10:9 KJV, but he didn't do anything else, do you think he was saved?
No sense in answering absent of also sharing the context within which I an answering you from.
Said context being that there were two groups of Believing Jews/Israelites during the 1st Century.
James mentions both groups to Paul, in the following exchange between them.
Acts 21:18 And the day following Paul went in with us unto James; and all the elders were present. 21:19 And when he had saluted them, he declared particularly what things God had wrought among the Gentiles by his ministry.
Group One:
21:20 And when they heard it, they glorified the Lord, and said unto him, Thou seest, brother, how many thousands of Jews there are which believe; and they are all zealous of the law:
Group Two:
21:21 And they are informed of thee, that thou teachest all the Jews which are among the Gentiles to forsake Moses, saying that they ought not to circumcise their children, neither to walk after the customs.
That Second Group had been converted by Paul and or one or another of his co-laborers, and were as the Gentiles converted by Paul and or by one or another of his co-laborers.
Such Jews/Israelites that James' has just mentioned to Paul in verse 21 herein above that he and his group (James and company) has heard of, were as these Gentiles...
21:25 As touching the Gentiles which believe, we have written and concluded that they observe no such thing, save only that they keep themselves from things offered to idols, and from blood, and from strangled, and from fornication.
Here, for example, is a writing to, and a description of, by Paul, of this Second Group of 1st Century Believing Jews/Israelites - but among the Gentiles: Jews/Israelites who, unlike James' Group, were taught by Paul that they were not...under The Law...
Romans 7:1 Know ye not, brethren, (for I speak to them that know the law,) how that the law hath dominion over a man as long as he liveth?
7:4 Wherefore, my brethren, ye also are become dead to the law by the body of Christ; that ye should be married to another, even to him who is raised from the dead, that we should bring forth fruit unto God. 7:5 For when we were in the flesh, the motions of sins, which were by the law, did work in our members to bring forth fruit unto death. 7:6 But now we are delivered from the law, that being dead wherein we were held; that we should serve in newness of spirit, and not in the oldness of the letter.
Of course, this was due to a change in Economy, Stewardship, or Dispensation...
From Prophecy (Israel: concerning that which was Prophesied since the world began, Acts 3:21) to Mystery (the Body: concerning that which was Kept Secret since the world began, Rom. 16:25).
As with any New Administration, remnants of the Old remain for a time, gradually diminishing away, as the New one, eventually surpasses every aspect of it that had applied only in a prior Dispensation, or Economy.
However, the assertion that this diminishing away of that which had been Prophesied was more and more superseded by that which had been Kept Secret, is not to say that God was now through with that "short work upon the earth" concerning Israel which He had Prophesied He will one day yet bring to come to pass...
Romans 9:27 Esaias also crieth concerning Israel, Though the number of the children of Israel be as the sand of the sea, a remnant shall be saved: 9:28 For he will finish the work, and cut it short in righteousness: because a short work will the Lord make upon the earth. 9:29 And as Esaias said before, Except the Lord of Sabaoth had left us a seed, we had been as Sodoma, and been made like unto Gomorrha.
Romans 11:12 Now if the fall of them be the riches of the world, and the diminishing of them the riches of the Gentiles; how much more their fulness?
Romans 11:25 For I would not, brethren, that ye should be ignorant of this mystery, lest ye should be wise in your own conceits; that blindness in part is happened to Israel, until the fulness of the Gentiles be come in. 11:26 And so all Israel shall be saved: as it is written, There shall come out of Sion the Deliverer, and shall turn away ungodliness from Jacob: 11:27 For this is my covenant unto them, when I shall take away their sins.
The result being that with the TEMPORARY interruption of that which had been Prophesied, one finds a diminishing away of its' Economy or Dispensation that results in a remnant of the prior one, for a time.
Case in point...
Acts 18:24 And a certain Jew named Apollos, born at Alexandria, an eloquent man, and mighty in the scriptures, came to Ephesus. 18:25 This man was instructed in the way of the Lord; and being fervent in the spirit, he spake and taught diligently the things of the Lord, knowing only the baptism of John. 18:26 And he began to speak boldly in the synagogue: whom when Aquila and Priscilla had heard, they took him unto them, and expounded unto him the way of God more perfectly.
That right there is a description of an individual who was behind in his understanding - BY DECADES - all the way back to BEFORE the Lord even BEGAN His ministry to Israel "AFTER that John was put in prison" Mark 1:14, 15.
To answer your question in light of my above...
"Hey Danoh do you think that if a believing Israelite, such as the ones to whom James and Peter wrote their epistles, and Jude---if one of them did Romans 10:9 KJV, but he didn't do anything else, do you think he was saved?"
My answer is that it depends on which group that applied to, and also, on how exactly it might have, or not.
And I already answered a part of that.
Acts 17:11, 12.