Based on the above, not only does the system of doctrine presented in the Westminster Standards leave room for a vigorous and Biblical view of the sacraments and sacramental efficacy, but practically demands it
The Sacraments
A sacrament, according to our Confession, is not simply a tangible token of a Spiritual truth, but consists of both the sign and the actual grace which is signified by the sign. These two elements are bound together by "a spiritual relation, or sacramental union" (27.2).
The sacraments serve as markers identifying their participants with the Church as opposed to the world (27.1). Since outside the Church there is no ordinary possibility of salvation, this in itself is quite an important point.
But sacraments also efficaciously exhibit and confer grace, not "by any power in them," nor by virtue of "the piety or intention of him that doth administer" them, but by virtue of "the work of the Spirit and the word of institution." To those who receive the sacrament worthily by faith there is a "promise of benefit" (27.3). This simply follows from the definition of a sacrament as both sign and thing signified united by the Spirit.
Thus, not only do the sacraments "strengthen and increase [the] faith" of "those within the covenant of grace," but they actually "signify, seal and exhibit . . . the benefits of [Christ’s] mediation" (Larger Catechism, q. 162). Thus, redemption itself is sealed and exhibited to us in the sacraments. The sacraments ability to "confirm our interest in" Christ, depends precisely on their role in efficaciously conferring that interest. Our faith is strengthened and increased precisely because we know in the sacrament we objectively experience "the working of the Holy Ghost" (LC, q. 161).
What is the nature of the grace conferred by the sacraments? Jesus Christ Himself: "Christ and the benefits of the new covenant are represented, sealed, and applied to believers" (SC, q. 92; emphasis added). Not simply the benefits of the new covenant, nor even the benefits of Christ, but "Christ and His benefits" are "the spiritual part of " the sacraments (LC, p. 176). The person of the Savior is "applied" to us by faith ("believers") in the sacraments. As discussed above, Christ’s benefits are not available apart from their Source. Christ’s benefits are applied to us precisely because Christ Himself is applied to us.
Putting it all together, in the sacraments Christ Himself is efficaciously communicated, represented, signified, sealed, conferred, and applied by the working of the Holy Spirit to those who receive Him by faith. Thus, the sacraments are "effectual means of salvation" (LC, p. 161).
Notice how the centrality of union with Christ, and the importance of the covenant, the institutional church, are both consistent with this view of the sacraments. Salvation results from Christ being applied to us by the Spirit; the sacraments are used by the Spirit to indeed apply Christ. Christ is received by faith; the sacraments exhibit Christ so that he may be apprehended by believers. Christ is offered "according to the Covenant of Grace" and calls people into the Church, His Kingdom; the sacraments are the objective means by which one is admitted into and continues in the Church.
These observations about the Westminster Standards and the sacraments in general, will be amply affirmed by a brief look at each sacrament in particular.
Baptism
Baptism admits the person baptized into the Church (28.1). This applies to both adults and infants. While the Catechism affirms that the children of a believer are "in that respect within the covenant" (LC, q. 166) this does not change the fact that children, like adult converts, are admitted into the Church by baptism.
The Westminster Confession of Faith guards against formulations that would mislead people into thinking that a person is automatically going to heaven once he is baptized no matter what he does subsequently. Of course, it also guards against the idea that all baptized people receive an identical portion of grace so that the difference between those who end up in heaven and those in hell is attributed to their own abilities and not the sovereignty of God in giving and withholding His grace. Thus, the Confession affirms that it is possible for people to be regenerated who are not baptized and that it is possible for people to not be regenerated who are baptized (28.5). Furthermore, it states that "the efficacy of Baptism is not tied to the moment of time wherein it is administered" (28.6).
But the Confession is emphatic that, despite all these qualifications, "yet notwithstanding, by the right use of this ordinance, the grace promised is not only offered, but really exhibited and conferred, by the Holy Ghost" (28.6). "Grace and salvation" are truly "annexed" to baptism (28.5).
What is the grace annexed to baptism? We have already seen that it would be the person of Christ himself, as is stated about the sacraments. The Confession lists these benefits of baptism: "the covenant of grace, ingrafting into Christ, of regeneration, of remission of sins and of his giving up unto God, through Jesus Christ, to walk in newness of life" (28.1). The Larger Catechism adds "adoption" and "resurrection unto everlasting life" (q. 165). All this is conferred by the Holy Spirit in Baptism.
One other qualification which needs to be mentioned is that baptism is said to savingly benefit "such (whether of age or infants) as the grace belongeth unto according tot he counsel of God’s own will, in his appointed time" (28.6). Here we seem to have a problem: The Divines wanted to affirm that baptism was efficacious, but not for everybody. Obviously, only the elect are finally saved and thus only the elect can be said to receive these things in baptism. But if that is the case, then how a person have his faith confirmed and strengthened by baptism? How can he trust a promise that might or not be made to him, depending on God’s secret counsel?
I’m not sure why the Divines did not directly address this question. However, they did write out how one should regard his baptism as an objective revelation of the Grace of God. The Larger Catechism, in the answer to question 167, spells out how baptism is supposed to be regarded by all who have been subjected to the rite.
The needful but much neglected duty of improving our baptism, is to be performed by us all our life long . . . by serious and thankful consideration of the nature of it, and of the ends for which Christ instituted it, the privileges and benefits conferred and sealed thereby, and our solemn vow made therein; by being humbled for our sinful defilement, our falling short of, and walking contrary to, the grace of baptism, and our engagements; by growing up to assurance of pardon of sin, and of all other blessings sealed to us in that sacrament; by drawing strength from the death and resurrection of Christ, into whom we are baptized, for the mortifying of sin, and quickening of grace; and by endeavoring to live by faith, to have our conversation in holiness and righteousness, as those that have therein given up their names to Christ; and to walk in brotherly love, as being baptized by the same Spirit into one body (emphasis added).
Here we see that baptism marks the objective starting point of the Christian life. There is no question that baptism has "conferred and sealed" grace. But that grace must be received by faith, and by continuing in the Faith. Remember q. 153 in the Larger Catechism:
That we may escape the wrath and curse of God due to us by reason of the transgression of the law, he requireth of us repentance toward God, and faith toward our Lord Jesus Christ, and the diligent use of the outward means whereby Christ communicates to us the benefits of his mediation.
The sacraments are listed as among those means in which all Christians must continue if they are to escape the wrath and curse of God. Baptism is not a sign that grace is conferred on somebody somewhere, but that it is specifically conferred on the person who is baptized. That grace, however, must be received by faith throughout the person’s life.
Perhaps we can help clarify this doctrine by using the statements on saving faith in 14.2 by analogy:
By this faith, a Christian believeth to be true and receiveth the grace of God promised and conferred in his Baptism, for the authority of God Himself speaking and efficaciously working therein, and acteth differently upon that which each aspect thereof demandeth; yielding obedience to the engagements made therein, walking in conformity to the grace of Baptism, trembling at the threatenings against those who would neglect so great a salvation , and embracing the promises of God for this life, and that which is to come. But the principal acts of saving faith are accepting, receiving, and resting upon Christ alone for justification, sanctification, and eternal life, by virtue of the covenant of Grace.
The gift of saving faith given by the Holy Spirit only to those elected to eternal life is not opposed to the objective grace conferred in baptism, but requires it. Faith needs an object. Faith apprehends Christ as He is exhibited to us in our baptism.
The Lord’s Supper
In the Eucharist, Participants by faith "really and indeed, yet not carnally and corporally but spiritually, receive, and feed upon, Christ crucified and all benefits of his death (29.7). The Shorter Catechism states that "worthy receivers" are "by faith, made partakers of his body and blood, with all his benefits to their spiritual nourishment, and growth in grace" (q. 96). Note, they are not said to receive the benefits of Christ’s body and blood, but Christ’s body and blood "with his benefits."
Again, the Westminster Divines guard against abuses and superstitions-denying any local presence as in transubstantiation and consubstantiation. Nevertheless, by the power of the Holy Spirit ("spiritually" twice in the paragraph) "the body and blood of Christ" are made "present" and received by faith (29.7). Thus, there is an objective "spiritual nourishment" and, therefore, a basis for "growth in grace" (q. 96). Partakers have their "union and communion with [Christ] confirmed" (LC, q. 169) because "truly and really" they "feed upon the body and blood of Christ" (LC, q 170).
Conclusion
The Westminster Standards give us a theology which demands and presents the sacraments as effectual signs which, by the power of the Holy Spirit, convey what they signify. Of course, without faith one will not apprehend the grace exhibited in the sacrament. But if the sacraments did not include the promised presence of Christ Himself then there would be nothing for believers to receive in partaking of them. Their faith would be in vain.
The sacraments are not empty signs, but are joined to the reality which they represent.
FOR FURTHER READING
Sacramental Assurance & the Reformed Faith: The Biblical Perspective of the Westminster Standards
Baptismal Efficacy & the Reformed Tradition: Past, Present, and Future