Powerfully (eutonōs). Adverb from eutonos (eu, well, teinō, to stretch), well-strung, at full stretch.
Confuted (diakatēlegcheto). Imperfect middle of the double compound verb diȧkaṫelegchomai, to confute with rivalry in a contest, here alone. The old Greek has dielegchō, to convict of falsehood, but not this double compound which means to argue down to a finish. It is the imperfect tense and does not mean that Apollos convinced these rabbis, but he had the last word.
Publicly (dēmosiāi). See note on Act 5:18; and note on Act 16:37. In open meeting where all could see the victory of Apollos.
Shewing (epideiknus). Present active participle of epideiknumi, old verb to set forth so that all see.
By the Scriptures (dia tōn graphōn). In which Apollos was so “mighty” (Act 18:24) and the rabbis so weak for they knew the oral law better than the written (Mar 7:8-12).
That Jesus was the Christ (einai ton Christon Iēsoun). Infinitive and the accusative in indirect assertion. Apollos proclaims the same message that Paul did everywhere (Act 17:3). He had not yet met Paul, but he had been instructed by Priscilla and Aquila. He is in Corinth building on the foundation laid so well by Paul (1Co 3:4-17). Luke has here made a brief digression from the story of Paul, but it helps us understand Paul better There are those who think that Apollos wrote Hebrews, a guess that may be correct.