"He also sealed us." It seems strange that so figurative a word should be used without a hint of explanation, and we must assume that it was so familiar in the Church that the right application could be taken for granted. The middle voice (σφραγισάμενος) makes it certain that the main idea is, "He marked us as His own." This is the sense in which the word is frequently used in the Book of Revelation: the servants of God are sealed on their foreheads, that they may be recognised as His. But what is the seal? Under the Old Testament, the mark which God set upon His people--the covenant sign by which they were identified as His--was circumcision. Under the New Testament, where everything carnal has passed away, and religious materialism is abolished, the sign is no longer in the body; we are sealed with the Holy Spirit of promise (Eph. i. 13 f.). But the past tense ("He _sealed_ us"), and its recurrence in Eph. i. 13 ("ye _were_ sealed"), suggest a very definite reference of this word, and beyond doubt it alludes to baptism. In the New Testament, baptism and the giving of the Holy Spirit are regularly connected with each other. Christians are born of water and of the Spirit. "Repent," is the earliest preaching of the Gospel (Acts ii. 38), "and be baptised every one of you, ... and ye shall receive the gift of the Holy Ghost." In early Christian writers the use of the word "seal" (σφραγίς) as a technical term for baptism is practically universal; and when we combine this practice with the New Testament usage in question, the inference is inevitable. God puts His _seal_ upon us, He _marks_ us as His own, when we are baptised.[11] 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.