'Certain' in the Bible

I went up [to Jerusalem] because of a [divine] revelation, and I put before them the gospel which I preach among the Gentiles. But I did so in private before those of reputation, for fear that I might be running or had run [the course of my ministry] in vain.

Before certain men came from James, he used to eat [his meals] with the Gentiles; but when the men [from Jerusalem] arrived, he began to withdraw and separate himself [from the Gentile believers], because he was afraid of those from the circumcision.