John 15 also will explain further what you are having difficulty in understanding.
There is a reason we are to REMAIN in HIM and not go out from HIM
Now, are all men in HIM?
No they aren't.
Therefore what can they do if it is done apart from HIM?
Nothing.
Therefore there is ONE DOCTRINE we are concerned with if we are seeking HIS WORK, HIS KINGDOM, and HIS RIGHTEOUSNESS...
And that was to point ALL men to THE DOOR...
But those who add to the foundation who go out from the DOCTRINE of CHRIST, who progress above HIM who is THE HEAD have forgotten the very first TRUTH of how they were even IN HIM to begin with.
Keep that ever before you.
If what you began in remains in you, you too will remain in BOTH the FATHER and the SON and this is what HE promised us...
Even ETERNAL LIFE.