In many ways, Ephesians is Paul's "summing-up" book. The same subjects appear in greater detail in books like Romans, 1 Corinthians, and 1 Thessalonians. But in Ephesians, Paul gives an overall view of the grand scheme of the gospel. Only now, Paul says, has God's hidden plan for all of history come to light.
Because it compresses such large thoughts into such a short space, Ephesians deserves very careful study. Read the first three chapters slowly, digesting one paragraph at a time. Such study will prove rewarding: Ephesians gives exuberant good news about the nature of the universe and God's plan for believers.
Like other letters from Paul, Ephesians divides fairly neatly between doctrine (chapters 1-3) and practical advice (4-6). The last half details how our lives should change as a result of the great things described in the first part.