The word “mystery” is often misunderstood in this context. It does not refer to something that is difficult to understand or designed to be a riddle; rather, it refers to almost the opposite. It is something that was concealed in the past but is now being revealed. God’s great desire is that we understand in a deeper and fuller way His great heart for the lost and the people of all nations, and in doing so, understand the ultimate purpose of the church. It was veiled before the incarnation and ministry of Christ, but now God has put it on full display and wants it to be known.