3:1 carnal. There is thus a distinction between “spiritual” believers and “carnal” believers, the one controlled by the Spirit, the other still largely controlled by the flesh (note Romans 8:5-13; Galatians 5:16-25). Carnal Christians are not necessarily unsaved pseudo-Christians, although they need to examine themselves carefully to determine whether their profession of faith in Christ is genuine (II Corinthians 13:5). Quite possibly they are just “babes in Christ” and need to “grow in grace and in the knowledge of our Lord and Saviour Jesus Christ” (II Peter 3:18).
3:2 not with meat. Compare Hebrews 5:12-14. Baby Christians are wonderful to see, just like baby people; but if they remain babies indefinitely, they become tragic to behold. Spiritual growth requires, first, the milk of the word (I Peter 2:2), but then soon they should begin to partake of the strength-building meat of the word (Jeremiah 15:16).