Our Lord clearly intimates that a person may be truly united to Him as the branch is to a tree that feeds it yet may be cut off later and cast into fire because he has not brought forth fruit to the glory of God. As the vinedresser will remove all branches that are dead or that bear no fruit, so will God take from His church all professed Christians who give no evidence by their lives that they are truly united to the Lord Jesus.
The person who does not bear fruit is first cut off from Jesus. This means he/she will have no relationship with Him again. After being cut off, he/she withers. To be withered is to be deprived of God’s grace. This will lead to becoming cold and insensitive to the Spirit. Then he/she is gathered by men which connote backsliding. The person becomes united with the world again because all his/her spiritual sensors become inactive. That person is cast into the fire that is, being separated from God and His people. The fate of the unfruitful believer may eventually be hell fire.
However, as the vinedresser prunes every branch that bears fruit, so God purifies all true Christians so that they may be more useful. He takes away that which hindered their usefulness, teaches them, quickens them, revives them, and makes them purer in motive and in life. He does it by taking away what opposes their usefulness.