When the New Testament addresses spiritual maturity, it uses the common Greek word teleios, which means “perfect” or “complete.” When it is applied to Christian growth, it indicates spiritual maturity in contrast to childlike immaturity as, for example, in this command from Paul: “Brothers, do not be children in your thinking. Be infants in evil, but in your thinking be mature (teleioi).” (1 Cor. 14:20; see also Heb.5:13–6:1). Sometimes it indicates perfection, as in Jesus’ summary command in the Sermon on the Mount: “You therefore must be perfect, as your heavenly father is perfect” (Matt.5:48). Spiritually, it always references solid, biblically informed understanding and conduct in Christ—spiritual adulthood.