Andrew Gray (Works, p. 195):
There are many [Christians] that are more desirous to know what they are, than what they should do: there are some that are more taken up to know whether they be justified and sanctified, than to be indeed justified and sanctified; and they are more desirous to know if they be in Christ, than indeed to be in him: and therefore, we do find many who do spend a great deal more time disputing that question,—whether am I in Christ or not?—than they do in using those means by which real union and communion with him may be attained: but Oh! will you once study to be more in him, and that shall be the shortest way to attain to the knowledge of your being in him.