Without experience (apeiro). Old adjective (alpha privative and peira, trial). Inexperienced. The babe (nhpio, old word, negative nh and epo, word like Latin infans, infant, not able to talk), not able to chew if one uses only milk and is without teeth. Perhaps moral truth is meant by "word of righteousness" (cf. 1 Corinthians 1:2 ; 1 Corinthians 2:3 for the word spoken by Christ).