From the Haydock Commentary:
Ver. 22. Receive ye the Holy Ghost. It was said, (John vii. 39.) that the Spirit was not yet given, because Jesus was not glorified. The sense must need be, that the holy Spirit was not given in that solemn manner, nor with so large an effusion of spiritual gifts and graces, till the day of Pentecost, after Christ’s ascension: but the just, at all times, from the beginning of the world, were sanctified by the grace of the Holy Ghost, as no doubt the apostles were, before this time. Now at this present, he gave them the power of forgiving sins. (Witham) — Some say, that our Saviour did not then confer the Holy Ghost on his disciples, but only prepared them for the receiving of the Holy Ghost. But surely we may understand, that even then they received some portion of spiritual grace, the power, not indeed of raising the dead, and working other miracles, but of forgiving sins. (St. Chrysostom, hom. lxxxv. in Joan.) — St. Cyril of Alexandria, speaking of the remission of sins, promised in this text, asks, “How then, or why, did Christ impart to his disciples a power, which belongs to the divine Spirit, should likewise possess the power of forgiving sins, and of retaining such as they judged expedient; that Holy Spirit, according to his good pleasure, forgiving and retaining, through the ministry of men.” (In Joan. lib. xii. chap. 1.)
From Matthew Henry’s Commentary:
The solemn grant he made, signified by this sign, Receive ye the Holy Ghost, in part now, as an earnest of what you shall further receive not many days hence.” They now received more of the Holy Ghost than they had yet received. Thus spiritual blessings are given gradually; to him that has shall be given.