12 The fellowship of this Holy Spirit He bestowed on the Apostles; for it is written, And when He had said this, He breathed on them, and says unto them, Receive the Holy Ghost: whose soever sins you remit, they are remitted unto them; and whose soever sins you retain, they are retained. This was the second time He breathed on man (His first breath having been stifled through wilful sins); that the Scripture might be fulfilled, He went up breathing upon your face, and delivering you from affliction. But whence went He up?
From Hades; for thus the Gospel relates, that then after His resurrection He breathed on them. But though He bestowed His grace then, He was to lavish it yet more bountifully; and He says to them, I am ready to give it even now, but the vessel cannot yet hold it; for a while therefore receive ye as much grace as you can bear; and look forward for yet more; but tarry ye in the city of Jerusalem, until ye be clothed with power from on high. Receive it in part now; then, you shall wear it in its fullness.
For he who receives, often possesses the gift but in part; but he who is clothed, is completely enfolded by his robe. “Fear not,” He says, “the weapons and darts of the devil; for you shall bear with you the power of the Holy Ghost.” But remember what was lately said, that the Holy Ghost is not divided, but only the grace which is given by Him.
Source: Catechetical Lectures (New Advent)