WTBTS teaches that the central theme of the Bible is God's Kingdom. Well, after reading the Bible for myself, I can say, most assuredly, that that is not the case. While the OT largely has prophecies relating to Christ, there is an even more overarching theme that I picked up on, and that is, very simply: take care of those who are less fortunate than you... widows, orphans, the poor. It's one of the main reasons Sodom was destroyed (Eze. 16:49), and it is named as the form of acceptable worship (James 1:27). The Mosaic Law has numerous portions in it related to this, and God removed his support of the Israelites for ignoring the poor among them.
If I were asked, what is the theme of the Bible, I would say (to quote Bill & Ted's Excellent Adventure): "Be excellent to each other!"
Does it prove inspiration? No. That isn't provable, in my opinion.