If we're predetermined to either be in God's Kingdom or not, what's the point?
The belief that God has already predetermined our lives and our rewards or punishments is a mistaken understanding of the subject of predestination.
Regarding predestination, Ephesians 1:5 tells us that God "predestined us to adoption as sons by Jesus Christ to Himself." Speaking of Christ, verse 11 says, "In Him also we have obtained an inheritance, being predestined according to the purpose of Him who works all things according to the counsel of His will." Romans 8:29-30 adds, "For whom He foreknew, He also predestined to be conformed to the image of His Son, that He might be the firstborn among many brethren. Moreover whom He predestined, these He also called; whom He called, these He also justified; and whom He justified, these He also glorified."
In reading these scriptures, there are two ways we can understand predestination. One way is to assume that God has everyone's life already planned out and that He already knows what we are going to do. Another way to understand predestination is from the perspective that God planned the purpose for human beings in the beginning (to become His sons and daughters), although He doesn't know what each of us will do. Let's consider a few additional scriptures to see which way we should understand these passages.
In Genesis 4 we read of God talking with Cain, who was upset that his offering was not accepted. God told him, "If you do well, will you not be accepted? And if you do not do well, sin lies at the door. And its desire is for you, but you should rule over it." If God had already predetermined what Cain would do, it would have been pointless to give Cain the advice to "rule over" sin. God gave Cain this advice and then allowed him to make his own decision.
This is free moral agency—the opportunity God gives us to make choices regarding what we will do. In Deuteronomy 30:19, God encouraged the ancient Israelites to "choose life"—that is, choose His way of life so they could receive blessings. Again, if God already knew what choice they would make, this encouragement would have been pointless.
In accordance with these passages (and many more throughout the Bible), we realize that God wants us to choose and live His way of life, but He doesn't know in advance what each of us will do.