But solid food belongs to those who are full age (spiritually mature), that is, those who by reason of use have their senses exercised to discern both good and evil. Therefore, leaving the discussion of the elementary principles (the baby stuff) of Christ, let us go on to perfection (Hebrews 5:14; 6:1).
It is the desire after holiness, the tender conscience that longs above everything to discern good and evil, the heart seeks only, and always, and fully to know and do the will of God, that marks the perfect (spiritually mature). The man who has set his heart upon being holy, and in the pursuit after the highest moral and spiritual perfection exercises his senses in everything to discern good and evil, is counted the perfect (spiritually mature) man. We read of God’s perfecting Christ through suffering. Perfection is that perfect union with God’s will, that blessed meekness and surrender to God’s will, which the Father wrought in Christ through His suffering. We read of Christ’s learning obedience, and so being made perfect. This is the true maturity or perfection, the true wisdom among the perfect, the knowing and doing of God’s will. – Andrew Murray