Sorry I'm so late in getting this up. I lost my notes, so I'm just going from memory here. Those who are in our Bible study, please feel free to add anything I missed from the study. We'd also love to hear thoughts from anyone else out there who is studying this as well.
we vs. you
Paul uses the word "we" in verse 12, and says "you", in verse 13. Who is he referring to in each? What is their purpose?
We concluded that the "we" is "the first to hope in Christ" (i.e. Paul and Jesus 1st apostles, etc.) The "you" would be both the Ephesians and all other believers. Both are intended to be for "the praise of His glory."
chiastic structure
Christopher pointed out that there seems to be a chiasm in verse 13. Here is an explanation of chiastic structure.
A: included in Christ
B: heard the word of truth
B: believed
A: marked with a seal
Holy Spirit:
The Holy Spirit is both a "deposit" and a "guarantee" of our inheritance. We receive the Holy Spirit when we believe and are included in Christ.