How does Saint Paul urge Christians to preserve ecclesial unity and put on the new man in Ephesians 4?

Writing from his place of confinement as a prisoner for the Lord, Paul urgently appeals to the Ephesian believers to conduct their lives in a manner worthy of their divine calling. He charges them to manifest profound humility, gentleness, and enduring patience, bearing charitably with one another's shortcomings and striving diligently to preserve the unity of the Spirit through the bond of peace.

The apostle articulates the sevenfold bedrock of Christian unity: there exists but one corporate body and one Holy Spirit, even as believers share one eternal hope attached to their calling; one Lord, one faith, one sacramental baptism; and one supreme God and Father of all, who is above all, through all and in us all.

Yet within this indivisible unity, distinctive graces are distributed to each individual according to the measure determined by Christ's generosity. Paul cites the prophetic psalm declaring that when the Victorious Messiah ascended on high, He led captive host into triumph and bestowed spiritual gifts upon humanity. The reality of His ascension necessarily implies that He first descended into the lower parts of the earth; thus, He who descended in humility is the identical Lord who ascended above the highest heavens, so that He might fill the entire cosmos with His sovereign presence.

Christ gave diverse offices within the Church, appointing some as apostles, others as prophets, evangelists, pastors, and authoritative teachers. A Challoner annotation highlights that Christ established this perpetual succession of legitimate pastors and spiritual guides to protect the flock from being blown about by every shifting wind of doctrine and to preserve the faithful in unity and truth. These ministries serve to equip the saints for pastoral service and build up the Body of Christ, until all believers arrive at complete harmony in faith and mature knowledge of the Son of God, attaining the full stature of Christ's maturity. Under this pastoral protection, believers will no longer resemble gullible infants tossed about by waves of human deception and cunning trickery. Instead, practicing authentic truth in divine charity, they grow upward into Christ the living Head, from whom the entire ecclesial body—harmoniously connected and supported by every supplying joint—increases and edifies itself in love according to the proportionate function of each part.

Paul solemnly commands them in the presence of the Lord to abandon forever the futile lifestyle characteristic of unregenerate Gentiles. Unbelievers live with intellects darkened by ignorance, alienated from the divine life because of deep-seated blindness and callousness of heart. Yielding to despair and moral recklessness, they plunge into unbridled sensuality, uncleanness, and insatiable greed. The Ephesians, however, did not learn Christ in this degraded fashion, provided they have truly heard His voice and received the genuine truth revealed in Jesus. They are called to strip away the old fallen nature inherited from their past conduct, which rots away under deceitful cravings, to experience spiritual renewal in the deepest inclinations of their minds, and to clothe themselves with the new man created in God's image in true justice and authentic sanctity.

This interior transformation translates directly into concrete social virtues. Believers must renounce falsehood and speak honest truth with their neighbors, remembering that they are fellow members of the same spiritual body. Paul says to be angry and not sin, nor permit the setting sun to witness lingering resentment, which surrenders ground to the devil. Any person who formerly stole must cease thievery, turning instead to honest physical labor so as to possess material goods to share with the destitute. Foul, destructive speech must never pass their lips; rather, their words should provide edification and convey grace to those who hear. Believers must take care never to grieve the Holy Spirit of God, whose seal marks them for the ultimate day of redemption. Every trace of bitterness, rage, wrathful shouting, abusive language, and spiteful malice must be eradicated, replaced by mutual kindness, tenderhearted mercy, and generous forgiveness modeled upon God's gracious pardon granted through Christ.