The fruit is the evidence we are abiding in the Vine.
Just my view:
This (like all who fall away) can be discerned by the parable of the sower.
Mat 13:18 Hear ye therefore the parable of the sower.
Mat 13:19 When any one heareth the word of the kingdom, and understandeth it not, then cometh the wicked one, and catcheth away that which was sown in his heart. This is he which received seed by the way side.
Mat 13:20 But he that received the seed into stony places, the same is he that heareth the word, and anon with joy receiveth it;
Mat 13:21 Yet hath he not root in himself, but dureth for a while: for when tribulation or persecution ariseth because of the word, by and by he is offended.
Mat 13:22 He also that received seed among the thorns is he that heareth the word; and the care of this world, and the deceitfulness of riches, choke the word, and he becometh unfruitful.
Mat 13:23 But he that received seed into the good ground is he that heareth the word, and understandeth it; which also beareth fruit, and bringeth forth, some an hundredfold, some sixty, some thirty.
The different types of believers:
Wayside believers
Stony soil believers
Unfruitful believers
Good soil believers
The question is what kind of believer are we going to be? Are we going to let the weeds of this world's system choke out our love for Christ? Or are we going to submit our hearts to some Holy Spirit plowing and bare fruit for our Lord?
The fruit is the evidence we are abiding in the Vine.
If we choose not to abide in the Vine then we do not have the life of Christ and thus are not His.
