But the seal is not baptism as a ceremonial act. It is neither immersion nor sprinkling nor any other mode of lustration which marks us out as God's. The seal by which "the Lord knoweth them that are His" is His Spirit; it is the impress of His Spirit upon them. When that impress can be traced upon our souls, by Him, or by us, or by others, then we have the witness in ourselves; the Spirit bears witness with our spirits that we are children of God.
But of all words "spirit" is the vaguest; and if we had nothing but the word itself to guide us, we should either lapse into superstitious ideas about the virtue of the sacrament, or into fanatical ideas about incommunicable inward experiences in which God marked us for His own. The New Testament provides us with a more excellent way than either; it gives the word "spirit" a rich but definite moral content; it compels us, if we say we have been sealed with the Spirit, and claimed by God as His, to exhibit the distinguishing features of those who are His. "The Lord is the Spirit" (2 Cor. iii. 17). To be sealed with the Spirit is to bear, in however imperfect a degree, in however inconspicuous a style, the image of the heavenly man, the likeness of Jesus Christ. There are many passages in his Epistles in which St. Paul enlarges on the work of the Spirit in the soul; all the various dispositions which it creates, all the fruits of the Spirit, may be conceived as different parts of the impression made by the seal. We must think of these in detail, if we wish to give the word its meaning; we must think of them in contrast with the unspiritual nature, if we wish to give it any edge. Once, say, we walked in the lusts of the flesh: has Christ redeemed us, and set on our souls and our bodies the seal of His purity? Once we were hot and passionate, given to angry words and hasty, intemperate deeds: are we sealed now with the meekness and gentleness of Jesus? Once we were grasping and covetous, even to the verge of dishonesty; we could not let money pass us, and we could not part with it: have we been sealed with the liberality of Him who says, "It is more blessed to give than to receive"? Once a wrong rankled in our hearts; the sun went down upon our wrath, not once or twice, but a thousand times, and found it as implacable as ever: is that deep brand of vindictiveness effaced now, and in its stead imprinted deep the Cross of Christ, where He loved us, and gave Himself for us, and prayed, "Father, forgive them"? Once our conversation was corrupt; it had a taint in it; it startled and betrayed the innocent; it was vile and foolish and unseemly: are these things of the past now? and has Christ set upon our lips the seal of His own grace and truth, of His own purity and love, so that every word we speak is good, and brings blessing to those who hear us? These things, and such as these, are the seal of the Spirit. They are Christ in us. They are the stamp which God sets upon men when He exhibits them as His own.
The seal, however, has another use than that of marking and identifying property. It is a symbol of assurance. It is the answer to a challenge. It is in this sense that it is easiest to apply the figure to baptism. Baptism does not, indeed, carry with it the actual possession of all these spiritual features; it is not even, as an _opus operatum_, the implanting of them in the soul; but it is a divine pledge that they are within our reach; we can appeal to it as an assurance that God has come to us in His grace, has claimed us as His own, and is willing to conform us to the image of His Son. In this sense, it is legitimate and natural to call it God's seal upon His people.