He was speaking about the Spirit, whom those who believed in Him were later to receive. For the Spirit had not yet been given, because Jesus had not yet been glorified.
KJV
(But this spake he of the Spirit, which they that believe on him should receive: for the Holy Ghost was not yet [given]; because that Jesus was not yet glorified.)
ASV
But this spake he of the Spirit, which they that believed on him were to receive: for the Spirit was not yet given; because Jesus was not yet glorified.