Paul visited Ephesus towards the end of his second missionary journey, leaving Priscilla and Aquila behind (Acts 18:18–19; maybe AD 51). They likely evangelized in Ephesus, and Apollos made some disciples as well (cf. Acts 18:24–19:7). Paul returned (maybe AD 54) to find a core of believers (Acts 19:1–7), evangelized further (Acts 19:8–10), and saw the hand of God at work (Acts 19:11–20; cf. 19:10, 20). The unbelievers there greatly opposed the gospel (Acts 19:21–41; 20:19), and Paul left shortly thereafter (Acts 20:1). He later bid farewell to the Ephesian elders at Miletus during later travels (Acts 20:17–38). Paul had lived Ephesus for three years (Acts 20:31). 

Paul wrote Ephesians during his first Roman imprisonment (Acts 28:30–31; AD 61). Tychicus, likely an Ephesian (cf. Acts 20:4), carried this letter (Ephesians 6:21–22) along with Colossians (Colossians 4:7–8) and Philemon (cf. Colossians 4:9 with Philemon 10). 

Paul likely heard (cf. Ephesians 1:15) from Tychicus (cf. Ephesians 6:21–22) how the Ephesians were doing and of their angst for him in prison (cf. Ephesians 3:1, 13). Having known them for 6 or 7 years, and having been with them for just under half of that time, Paul wrote to encourage them in a very doctrinal and practical way—his suffering was for their glory and the promotion of the gospel (Eph 3:13, 6:19–20).

One way to summarize Ephesians is this: “You are in Christ. Know what this means, and walk like Him.” We wish all the faithful in Christ grace and peace (Ephesians 1:1–2) and especially bless the Father for all the salvation blessings that He gives in Christ (Ephesians 1:3–14). Knowing these blessings, we should pray for one another to better understand the hope, riches, and power that are to us through Christ (Eph 1:15–23). Whereas we were once dead in sins, God made us live in Christ in order to know His saving grace forever (Ephesians 2:1–10). As Gentiles, our new life resulted in peace with God and becoming joint-citizens with all in the household of God (Ephesians 2:11–21). This display of God’s wisdom is the basis whereby we pray for one another to be spiritually strengthened in order to understand fully the love of Christ to us (Ephesians 3:1–21). United in salvation, we must walk together in unity, serve according to God’s grace to each of us, and thereby bring all to maturity in Christ (Ephesians 4:1–16). We therefore walk not as we were without Christ but with love, being like Him in every way (Ephesians 4:17–5:2). We walk not in darkness but wisely, as children of light who are filled with the Spirit (Ephesians 5:3–21). This Spirit-filled walk extends to how we relate as husbands and wives (Ephesians 5:22–33), children and fathers (Ephesians 6:1–4), and servants and masters (Ephesians 6:5–9). We stay strong in the Lord by wearing His armor (Ephesians 6:10–20), and we encourage one another and wish each other peace, love, faith, and grace (Ephesians 6:21–24).