John 8:31

Then said Jesus to those Jews that believed on him
For he knew instantly who they were, and when they believed on him; and therefore he immediately turned himself to them, and thus addressed them;

if ye continue in my word;
meaning the Gospel, called his, because he was both the author, and preacher, and sum, and substance of it: and to continue in it, is having cordially received it, to abide by it, and hold it fast, and not to be moved from it, by the temptations of Satan; the cunning of those that lie in wait to deceive; nor by the revilings and persecutions, the frowns and flatteries of men: and when men continue thus steadfast in it, and faithful to it, it is an evidence that it has come with power, and has a place in their hearts, and that they are the true followers of Christ:

then are ye my disciples indeed;
there are two sorts of disciples of Christ; some are only nominal, and merely in profession such; and these sometimes draw back from him, discontinue in his word, and go out from among his people; which shows that they never were of them, nor are the true disciples of Jesus; for the genuine disciples of Christ continue in his Gospel, hold fast to him, the head, and remain with his people; which to do to the end, is an evidence, of their being disciples indeed.