In the description of the guilt incurred by an apostate from Christ to Judaism is found another phrase descriptive of the Holy Spirit as the Spirit of grace (Heb. x. 29). If this is not the irremissible sin, it is sin at its climax. The Son of God is trampled down with ruthless scorn and hatred, His "precious blood" is counted as that of either an ordinary man or that of a guilty criminal. Then the description reaches the summit of wickedness, the sin of all sins, the irremissible sin — "and insulted the Spirit of grace." Most modern exegetes say that the Spirit is thus called because He is the gift of grace. But by referring to Zechariah xii. 10 we find the expression "Spirit of grace and supplication," evidently implying that the Spirit is "the source of grace" and the inspirer of all true prayer (Delitzsch). [The Spirit] is the source of grace not only in His own person, but He is the channel through which the love of the Father and the grace of His Son are poured upon penitent believers.
The importance of the Spirit's office in human salvation cannot be overestimated. The Father's love and the Son's self-sacrifice in the scheme of redemption are ineffectual without the Spirit's personal agency in applying the provisions of salvation. He is the appointed and indispensable almoner of the divine bounty and messenger of the King's pardon. If a city has a bureau of charities, its poor who proudly refuse its help and rely on the general benevolence of the city government, and starve because of their folly, are no more unreasonable than are those who admit that they are sinners, but are trusting in the fatherhood of God for forgiveness, ignoring His bureau of pardon, through the mediation of His Son, as administered by His accredited commissioner, the Spirit of Grace. Many Christians who are almost destitute of Spiritual strength might become strong through the more abundant life which Christ came to bestow, if they would honor with an intelligent faith that personality whom He has appointed as the Lord and giver of life.
— The Gospel of the Comforter (1898) Chapter 1.