A.T. Robertson Commentary Acts 18:28

"for he powerfully confuted the Jews, [and that] publicly, showing by the scriptures that Jesus was the Christ." — Acts 18:28 (ASV)

Powerfully (ευτονως). Adverb from ευτονος (ευ, well, τεινω, to stretch), well-strung, at full stretch.

Confuted (διακατηλεγχετο). Imperfect middle of the double compound verb δια-κατ-ελεγχομα, to confute with rivalry in a contest, here alone. The old Greek has διελεγχω, 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 (δημοσια). See 5:18; 16:37. In open meeting where all could see the victory of Apollos.

Shewing (επιδεικνυς). Present active participle of επιδεικνυμ, old verb to set forth so that all see.

By the Scriptures (δια των γραφων). In which Apollos was so "mighty" (verse 24) and the rabbis so weak for they knew the oral law better than the written .

That Jesus was the Christ (εινα τον Χριστον Ιησουν). Infinitive and the accusative in indirect assertion. Apollos proclaims the same message that Paul did everywhere (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 (1 Corinthians 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.