David wants to make public now the message that he received from the Lord privately which was that Solomon is the one who will build the temple of the Lord. As David says in this chapter the reason why he was not chosen is because: "You are a warrior and have shed blood." Instead Solomon was chosen to not only build the courts but God is going to make Solomon his son and he will be a father to him. From this time forward we find God wanting and desiring a personal relationship with His people and also wanting His people to desire a personal relationship with Him. This closeness is unmatched in any other religion. We serve a God who loves us and wants us to love Him.
I also find it interesting that David already has all the details worked out and the blueprints are ready to go. Solomon really isn't able to put his own creative spin on what the house of the Lord ought to look like because David and God have already worked it out the way that it ought to be. David also addresses his son Solomon and tells him to be strong and to act. Don't be a withering violet. I think that's a thing, I don't think I just made that up.
I love vs.9 where David states: "The Lord searches every mind, and understands every plan and thought." That ought to provide comfort and consolation for each of us as we look to do God's will and be sure that we are not just doing our own will.