Here is a good excerpt from the PDF about what the Kingdom of God is NOT properly:
1. The Church militant in this age
2. The rule of God in the hearts of believers
3. An spiritual rule to be consummated in an earthly millennial reign
4. A geo-political or social program in this age or a program of Christianizing all spheres of life
5. However: the power and influence of the kingdom is currently felt in these areas.
S. M. Baugh has also written a Greek Grammar for New Testament Greek. I own a copy and have found it to be a very enjoyable book to work through. Here is a link to his Grammar: