In this chapter, David officially appoints Solomon to build the temple in the presence of all Israel's national leaders.
This chapter is a natural conclusion to the previous five chapters of 1 Chronicles. So much of Chronicles is detailing David's vast preparations for the temple, in terms of the wars that he fought, the resources that he prepared, and the organization and planning that he performed, but with the ever-present caveat that he would not be permitted to build the temple himself. There isn't really any summary of the wars, but in this chapter David goes through the organization and planning and gives it all to Solomon. In the next chapter, David gives Solomon the resources and materials for the temple. This appears to be another chiasmus (discussed earlier in my commentary), since the preceding chapters discuss resources, Levites/priests, and commanders in that order. In this chapter (and the one that follows), David gives to Solomon the commanders (v. 1), the Levites/priests (v. 13) and the resources (1 Chron 29:2-5) in that order. This order inversion is typical of a chiasmus.
In addition, David gives to Solomon all of the plans for the temple, which he received as a divine insight from the spirit of God (v. 12, 19). This seems to be intended as an allusion to Moses, who went up the mountain to receive the plans for the tabernacle from the LORD as a divine revelation. Much as people remember Moses for bringing down the ten commandments, the section on the tabernacle and the furnishings therein was actually substantially longer than even the legal portion of Exodus. If you don't believe me, go and read Exodus 25-30. Not only is David claiming to have divine revelation, even the list of things that he tells Solomon to construct are largely the same as what Moses was building (altars, lampstands, tables and utensils, and so on). In conclusion, this chapter is deliberately posturing David as a type of Moses. I'm not sure I entirely understand the motivation, but that is certainly what's happening from a literary perspective.
I also think this chapter is similar to Joshua 1 when Moses dies and the LORD urges Joshua to take the people into the promised land. This chapter is also a transition of power between David and Solomon. More specifically, this chapter contains a very similar refrain that Solomon should be "strong and courageous... do not be afraid or discouraged, for the LORD God, my God, is with you." (v. 20). This is an almost word-for-word copy of Joshua 1:9 when the LORD says to Joshua, "Be strong and courageous. Do not be terrified; do not be discouraged, for the LORD your God is with you wherever you go."
This parallelism would encourage us to view David as a kind of Moses and Solomon as a kind of Joshua. Ironically, Joshua was the man of war who invaded the promised land and now Solomon is the man of peace, so that kind of breaks the metaphor, but even so I think it's clear this is the metaphor that Chronicles is trying to portray.
This story is the same transition of power as in 1 Kings 1-2, but the rendition could not possibly be more different. If you read through 1 Kings 1-2, you basically see 4 different elements.
1) David is old and bedridden;
2) Adonijah challenges Solomon's claim to the throne;
3) David charges Solomon to obey the LORD, but not a single word about the temple;
4) David demands (and Solomon delivers) retribution upon his numerous enemies.
In this chapter, which is ostensibly the same series of events, you see:
1) "David rose to his feet" to present Solomon to his officials (v. 2);
2) Adonijah is not present;
3) David speaks at length to Solomon, both charging him to obey the LORD and also charging him to build the temple;
4) David does not mention a single one of his personal enemies.
This is a stark contrast where much of the focus shifts from David's retribution upon his personal enemies to David's vision for the temple and Solomon's role in it. This is a microcosm of the general differences between Samuel/Kings and Chronicles; Samuel and Kings are largely a narrative about the struggles and crises during David's kingship, while Chronicles is largely a narrative about the temple. Chronicles does not deny the struggles and crises occurred (there are a handful of implicit references to David's battles), but it certainly does not belabor them.
In the next chapter, the transition of power continues as David gives the resources for the temple to Solomon and Solomon is anointed king before all the people.