2:4 living stone. As not just the foundation rock (I Corinthians 3:11), but also as a living stone that could bring life and sustenance, Christ is the fulfillment of the type suggested by the rock smitten in the wilderness, which thenceforth brought life-sustaining water to God’s people (see Exodus 17:6; Numbers 20:8; I Corinthians 10:4).
2:4 chosen of God. The Greek word here for “chosen” (also in I Peter 2:9) is the same as that for “elect” in I Peter 1:2 and 2:6. Thus, the “elect of God” are those “chosen by God.” Note also John 15:16 and Ephesians 1:4.
2:6 chief corner stone. Note that Peter here recognizes that Christ, not himself, is the foundation stone of the church (as some have misinterpreted the teaching of Matthew 16:18). He is quoting from Isaiah 28:16, showing that this Messianic prophecy was fulfilled in Christ. The Lord Jesus also called His words the true foundation (Matthew 7:24-27) and Paul confirmed that there is no other foundation (I Corinthians 3:11). Isaiah had also stressed that “in the LORD JEHOVAH is everlasting strength,” or “the Rock of ages” (Isaiah 26:4).
2:6 be confounded. “Make haste” in Isaiah 28:16 is interpreted by Peter as “be confounded,” meaning “be ashamed.”