Ephesians 3 begins with the dispensation of grace that was given by God to Paul for us. Leviticus begins with the sacrifices and offerings that were ordained by God for the Priests to keep for us. Ephesians 3 talks about what has been made known to the apostles and prophets, and how he has been made a minister. Leviticus gives the instructions from Moses to the levitical priests and also to Aaron. Ephesians 3 says that the revelation that Jesus' sacrifice is for the Gentiles as well as the Jews was not made known in previous generations. There is no hint in Leviticus that the Gentiles will be included. We do not learn that Jesus is the Lamb of God that takes away the sin of the world until we get to the New Testament.