A.T. Robertson Commentary Romans 1:16

"For I am not ashamed of the gospel: for it is the power of God unto salvation to every one that believeth; to the Jew first, and also to the Greek." — Romans 1:16 (ASV)

It is the power of God (δυναμις θεου εστιν). This Paul knew by much experience. He had seen the dynamite of God at work.

To the Jew first, and also to the Greek (Ιουδαιω τε πρωτον κα Hελλην). Jesus had taught this (John 4:22; John 10:16; Luke 24:47; Acts 1:8). The Jew is first in privilege and in penalty (Romans 2:9f.). It is not certain that πρωτον is genuine, but it is in 2:9f.