And grieve not the Holy Spirit of God. Very solemn and emphatic counsel. The name is given with unusual fullness, in order to show the magnitude of the sin— τὸ πνεῦμα τὸ ἅγιον τοῦ θεοῦ, "The Spirit, the Holy Spirit of God."
By an anthropopathy the Spirit is represented as grieved by such treatment as would grieve us—e.g. when his work is obstructed, when sin is trifled with, when Deity is treated carelessly, when place is given to the devil, when the spirit of the world is cherished.
Those who act thus resemble the Sanballats and Tobiahs of the time of the restoration, who hindred the rebuilding of the temple and the restoration of order and prosperity. When the Holy Spirit would urge consecration, separation from the world, holy exercises, active service, our indolent and worldly hearts are liable to rebel and vex him.
To grieve a parent heedlessly is a great sin; how much more to grieve the Spirit of God? In whom ye were sealed unto the day of redemption. The Spirit being rather the Seal than the Sealer, who is the Father (see Ephesians 1:13), it is better to translate in whom than by whom; besides, this preserves the force of the ἐν, which, whether used of Christ or of the other persons of the Godhead, is so characteristic of the Epistle.
To grieve the Spirit is to help to obliterate the seal, and thus weaken the evidence of our redemption.