Acts 15:13-21 And after they had held their peace, James answered, saying, Men and brethren, hearken unto me:
Simeon hath declared how God at the first did visit the Gentiles, to take out of them a people for his name. And to this agree the words of the prophets; as it is written, After this I will return, and will build again the tabernacle of David, which is fallen down; and I will build again the ruins thereof, and I will set it up (Amos 9:11):
That the residue of men might seek after the Lord, and all the Gentiles, upon whom my name is called, saith the Lord, who doeth all these things (Amos 9:12).Known unto God are all his works from the beginning of the world. Wherefore my sentence is, that we trouble not them, which from among the Gentiles are turned to God:
But that we write unto them, that they abstain from pollutions of idols, and from fornication, and from things strangled, and from blood. For Moses of old time hath in every city them that preach him, being read in the synagogues every sabbath day.
This pronouncement was being sent to gentiles. James did not say 'follow the ten commandments and all the law and the prophets or your salvation will be cancelled'. Yet that is precisely what Mormonism teaches!
'Abstain from pollution of idols' is an interesting point, because later we find that Paul explains some (himself included) may have eaten food that had been offered to idols, but it didn't cancel his Salvation!
Abstain from fornication was perhaps an admonishment to not have pre-marital sex because such behavior has been frowned upon by God from the beginning, yet even this behavior is not a condition posed by which these gentile Christians would lose their Salvation.
The last two items are how we know this was aimed at trying to not cause contention between Jews converted to Christianity and the gentiles. Paul later addresses the freedom of Christians juxtaposed with the legalism of judaizers (Mormons).
Yet that is precisely what Mormonism teaches!
Joseph Smith