The normal way to find out what a Bible passage means is to look at a Bible Commentary. These are detailed books, explaining each passage of the Bible. Any Christian bookstore will have many to choose from. There are also a number online, though they tend to be old ones that have gone out of copyright.
I'm going to direct you to Matthew Henry's Commentary, who is well-known and generally reliable. Some of the things he says may have been superceded by more up-to-date scholarship, but for something like this he is pretty solid.
This parable primarily refers to the nation and people of the Jews. God chose them for his own, made them a people near to him, gave them advantages for knowing and serving him above any other people, and expected answerable returns of duty and obedience from them, which, turning to his praise and honour, he would have accounted fruit; but they disappointed his expectations: they did not do their duty; they were a reproach instead of being a credit to their profession. Upon this, he justly determined to abandon them, and cut them off, to deprive them of their privileges, to unchurch and unpeople them; but, upon Christ’s intercession, as of old upon that of Moses, he graciously gave them further time and further mercy; tried them, as it were, another year, by sending his apostles among them, to call them to repentance, and in Christ’s name to offer them pardon, upon repentance.
That is the exposition - i.e. what the passage meant when it was written. It is also a reasonable interpretation for us to take this warning for ourselves - that God expects us to "bear fruit", and there may be consequences if we don't.