Albert Barnes Commentary Acts 6:10

"And they were not able to withstand the wisdom and the Spirit by which he spake." — Acts 6:10 (ASV)

To resist. That is, they were not able to answer his arguments.

The wisdom. This properly refers to his knowledge of the Scriptures; his skill in what the Jews esteemed to be wisdom—acquaintance with their sacred writings, opinions, etc.

And the spirit. This has been commonly understood as the Holy Spirit, by whom he was aided; but it rather means the energy, power, or fervor of Stephen. He displayed a spirit of zeal and sincerity that they could not withstand; which served, more than mere argument could have done, to convince them that he was right. The evidence of sincerity, honesty, and zeal in a public speaker will often go further to convince most people than the most able argument, if delivered in a cold and indifferent manner.