Gregory the Great — as excerpted in the Catena Aurea on John 14:15-17

“(ii. Mor.) But if the Holy Spirit abides in the disciples, how is it a special mark of the Mediator that He abides in Him. (supr. 1:32. ἐπʼ αὐτὸν) We shall better understand, if we distinguish between the different gifts of the Spirit. In respect of those gifts without which we cannot attain to salvation, the Holy Spirit ever abides in all the Elect: but in respect of those which do not relate to our own salvation, but to the procuring that of others, He does not always abide in them. For He sometimes withdraws His miraculous gifts, that His grace may be possessed with humility. Christ has Him without measure and always.”