What had the Judean believers heard about Paul before he returned?

The Judean believers had heard only that the one who formerly persecuted them and tried to stamp out Jewish believers of the Messiah was now preaching the faith concerning Jesus the Lord Christ, which once he destroyed. They knew of his past opposition and his present preaching.

Les explains that these Jewish believers in Jerusalem and Judea had received only one report about the man: he who had persecuted them in times past and tried to stamp out Jewish believers of the Messiah was now preaching the faith concerning Jesus the Lord Christ—the very faith he once destroyed. This fits the context that he had no ministry to the Jews in Judea; he had gone into Gentile territory in Cilicia and Tarsus, a complete fork in the road from the twelve.

Galatians 1:23

But they had heard only, That he which persecuted us in times past now preacheth the faith which once he destroyed.

What had the Jewish believers in Judea heard about Paul's preaching?

The Jewish believers in Judea had heard only that the man who once persecuted them was now preaching the faith concerning Jesus the Lord Christ, the faith he had formerly tried to destroy. They knew of his past persecution and his complete reversal.