1)
What is the difference between a wife and a Pilegesh?
1.
Refer to Shoftim 8:31:1:1,2 and the notes there. A wife has Kidushin and Kesuvah.
2)
Here it says that David married other wives and concubines. Why does it say in Divrei ha'Yamim I, 14:3 only wives?
1.
Abarvenel: Because a concubine has Kidushin, she is called a wife. Malbim - this opinion can say that here they are called concubines because they do not have Kesuvah.
2.
Chomas Anach (here and Divrei ha'Yamim I, 14:3): It is for the honor of David. Here it mentions concubines first, for this was a Chidush. Only now that he became king [over all Yisrael], he was permitted to take concubines, like the Rambam says.
