Albert Barnes Commentary 2 Samuel 23:20

"And Benaiah the son of Jehoiada, the son of a valiant man of Kabzeel, who had done mighty deeds, he slew the two [sons of] Ariel of Moab: he went down also and slew a lion in the midst of a pit in time of snow." — 2 Samuel 23:20 (ASV)

Benaiah the son of Jehoiada - He commanded the Cherethites and Pelethites throughout David’s reign (2 Samuel 8:18; 2 Samuel 20:23). He also took a prominent part in supporting Solomon against Adonijah when David was dying and was rewarded by being made commander of the army in place of Joab (1 Kings 1:8, 26, 32-40; 2:25-35; 4:4). It is possible that his father, Jehoiada, is the same person mentioned in 1 Chronicles 12:27 as the leader of the Aaronites, since “Benaiah the son of Jehoiada” is called a “chief priest” (1 Chronicles 27:5).

Two lion-like men - The Hebrew word אריאל 'ărı̂y'êl literally means “lion of God” and is interpreted to mean “an eminent hero.” Instances occur among Arabs and Persians where the title “lion of God” was given to great warriors. For this reason, it is supposed that the same custom was prevalent among the Moabites. The Vulgate, however, translates this as “two lions of Moab,” a reading which seems to be supported by the next sentence.

Slew a lion... - Rather, this could refer to the lion—one of those described above as a “lion of God”—if the Vulgate’s translation is correct. Apparently, during a severe winter, a lion came up from its usual haunts to a village in search of food. It took possession of the tank or cistern, terrifying the inhabitants, and Benaiah boldly attacked and killed it.