For the Jews require a sign - A miracle, a prodigy, an evidence of divine interposition. This was the characteristic of the Jewish people. God had manifested himself to them by miracles and wonders in a remarkable manner in past times, and they greatly prided themselves on that fact, and always demanded it when any new messenger came to them, professing to be sent from God. This propensity they often evinced in their contact with the Lord Jesus; Matthew 12:38; Matthew 16:1; Mark 8:11; Luke 11:16; Luke 12:54-56. Many mss., instead of “sign” here in the singular, read “signs” in the plural; and Griesbach has introduced that reading into the text. The sense is nearly the same, and it means that it was a characteristic of the Jews to demand the constant exhibition of miracles and wonders; and it is also implied here, I think, by the reasoning of the apostle, that they believed that the communication of such signs to them as a people, would secure their salvation, and they therefore despised the simple preaching of a crucified Messiah. They expected a Messiah that should come with the exhibition of some stupendous signs and wonders from heaven (Matthew 12:38, etc., as above); they looked for the displays of amazing power in his coming, and they anticipated that he would deliver them from their enemies by mere power; and they, therefore, were greatly offended 1 Corinthians 1:23, by the simple doctrine of a crucified Messiah.
And the Greeks ... - Perhaps this means the pagan in general, in opposition to the Jews; see the note at Romans 1:16. It was, however, especially the characteristic of the Greek philosophers. They seek for schemes of philosophy and religion that shall depend on human wisdom, and they therefore despise the gospel.