The answer to the above questions is found in verses such as the following:
. . . no one can come to Me, unless it has been granted him from the Father. (NASB) John 6:65
No one can come to Me, unless the Father who sent Me draws him; and I will raise him up on the last day. (NASB) John 6:44
All that the Father gives Me shall come to Me, and the one who comes to Me I will certainly not cast out. (NASB) John 6:37
http://www.neverthirsty.org/pp/corner/read/r00257.html
All of these are true and I do not disagree with any of them nor am I attempting to show 1 John 3 is incorrect. However, we are addressing different situations. John is referring to those whose faith never took root. Apostasy addresses those who fully accept God's truth and then repudiate and renounce their faith.
John 15:1-8
15:1 "I am the true vine, and My Father is the vinedresser. 2 "Every branch in Me that does not bear fruit, He takes away; and every branch that bears fruit, He prunes it, that it may bear more fruit. 3 "You are already clean because of the word which I have spoken to you. 4 "Abide in Me, and I in you. As the branch cannot bear fruit of itself, unless it abides in the vine, so neither can you, unless you abide in Me. 5 "I am the vine, you are the branches; he who abides in Me, and I in him, he bears much fruit; for apart from Me you can do nothing. 6 "If anyone does not abide in Me, he is thrown away as a branch, and dries up; and they gather them, and cast them into the fire, and they are burned. 7 "If you abide in Me, and My words abide in you, ask whatever you wish, and it shall be done for you. 8 "By this is My Father glorified, that you bear much fruit, and so prove to be My disciples. NAS
What happens to a branch in the vine that ceases to be fruitful? How does a Christian become unfruitful?
Did you read the biography of Mel White? He is a modern example of one who walked away from abiding in Christ and is now teaching heresy in the guise of Christianity. He has ceased being fruitful by his choice and the Father will prune him from the vine.