4:13 and. “And” could better be rendered “even.” That is, the unity of the faith is essentially synonymous with “the knowledge of the Son of God.”
4:14 wind of doctrine. If this characteristic was true in the apostolic age, it is far more so today. The word “children” actually means “babes” (note Hebrews 5:13). The number of cults and heresies and compromises has multiplied almost without number, and vigilance against the crafty “deceiver,” Satan is needed more than ever (see note on Revelation 12:9).
4:15 truth in love. This is almost the antidote to false doctrine and even rank unbelief. “Speaking the truth” is actually one word in the Greek—“truth-speaking.” We should speak only if we speak the truth, remembering that “thy Word is truth” (John 17:17), and we should do so only in love (i.e., Christian charity, unselfish concern for those to whom we speak).