“By his cunning he will cause deceit to prosper under his hand.” In order to understand how the Antichrist will succeed, we must see the semantic range of some of the words in this phrase and also see the idiom involving “hand.” The word “cunning” (sekel #07922 שֶׂכֶל) can also mean “understanding” or “insight,” and it certainly means that here, but when used in a negative situation it also means “cunning,” “craftiness” (CJB), and even “treachery” (cp. NET).
The phrase “under his hand” (more literally “in his hand”), refers to both his own power and also his authority as exercised over others. Biblically, to be under someone’s hand is to be under their authority or power. So a very free and expansive translation of this verse could be something like: “The Antichrist will succeed in his purposes due to his understanding and insight and by virtue of the fact that he is cunning, deceitful and treacherous, and he will use his own power to accomplish his will and also accomplish his evil purposes through those he controls.”
“in his own mind.” The Hebrew is “in his heart,” but in this context it refers to his mind, what he thinks. The Hebrews did not know the function of the brain and assigned thinking to the heart. [For more on the use of the word “heart” in the Bible, see commentary on Prov. 15:21].
“in a time of peace.” The Hebrew is difficult due to the cryptic nature of the phrase, which is simply, “and in peace will destroy many.” This had led some translators say something like, “He will destroy many in a time of peace” (HCSB). However, there are other translators who think the phrase refers to the fact that the people are deceived into not expecting attack and thus are at peace themselves. So, for example, the NASB has, “And he will destroy many while they are at ease.”
It is likely that both meanings are true. The Antichrist makes a covenant with Israel, and that covenant no doubt promises peace (Dan 9:27). But he breaks the covenant and will attack without warning “in a time of peace.” However, during that time of peace, the people unwisely feel peaceful and safe but are attacked without warning (1 Thess. 5:3). Given that people are usually feeling peaceful and at ease in a time of peace, the REV reads “in a time of peace,” which certainly is true. The suddenness and ferocity of the attack is the reason that the ESV reads “without warning,” and while that is certainly true, that translation omits that it will be a time of peace, which we felt was important.
“but not by human power.” The Hebrew is more literally, “without hand he is broken” (YLT). In this context, the idiomatic use of “hand” refers to human power. The Antichrist will be broken, but not by any kind of regular earthly fighting; not by human armies. We learn from the New Testament that the Prince of Princes will use the spoken word to destroy the Antichrist and his system (2 Thess. 2:8; Rev. 19:15, 21).