At Ephesians 1:17 I have taken the position that it should be "the Spirit" rather than "a spirit." There are two reasons for my decision: 1. Paul already says that the Spirit aids us in discerning the things of God (1 Cor 2:14). 2. If we were to choose "a spirit" like most versions do, don't we still have to come back to the Spirit as the giver of wisdom and understanding into the things of God?