22:34 The climax of the chapter asserts that the altar was a witness … that the Lord is God. Previously, the chapter indicated only that it was to be a witness (vv. 27, 28), without saying what it would be a witness of. In a similar vein, Jesus told His disciples that people would know they were His disciples by seeing their love for each other; that is, their love would point people to Christ (John 13:35).
22:34 called the altar Witness. This sixth monument in the land (see note on 4:20) bears witness to the unity of the Transjordanian tribes with Israel west of the Jordan.
22:34 called the altar Naming an altar was a common practice after its creation in commemoration of some event or covenant. The actual name is not given here, but the account does note that whatever it was, it served as a witness to the tribes’ unity. See v. 10.
22:34 Witness. The altar witnessed (v. 27) to the one reality that united all Israel and, by implication, to the offense that could destroy Israel (v. 16).
 Sproul, R. C. (Ed.). (2005). The Reformation Study Bible: English Standard Version (p. 330). Orlando, FL; Lake Mary, FL: Ligonier Ministries.