What is a sacrament?
A sacrament is an holy ordinance instituted by Christ1; wherein, by sensible signs, Christ, and the benefits of the new covenant, are represented, sealed, and applied to believers2.
Scripture proofs
The Westminster Assembly's proof texts (KJV). The bracketed numbers in the answer above mark the clause each set of references supports; expand a row to read the verses.
1 Matt. 28:19; 26:26-28; Mark 14:22-25; Luke 22:19-20; 1 Cor. 1:22-26
Matt. 28:19 Go ye therefore, and teach all nations, baptizing them in the name of the Father, and of the Son, and of the Holy Ghost:
Matt. 26:26 And as they were eating, Jesus took bread, and blessed it, and brake it, and gave it to the disciples, and said, Take, eat; this is my body.
Matt. 26:27 And he took the cup, and gave thanks, and gave it to them, saying, Drink ye all of it;
Matt. 26:28 For this is my blood of the new testament, which is shed for many for the remission of sins.
Mark 14:22 And as they did eat, Jesus took bread, and blessed, and brake it, and gave to them, and said, Take, eat: this is my body.
Mark 14:23 And he took the cup, and when he had given thanks, he gave it to them: and they all drank of it.
Mark 14:24 And he said unto them, This is my blood of the new testament, which is shed for many.
Mark 14:25 Verily I say unto you, I will drink no more of the fruit of the vine, until that day that I drink it new in the kingdom of God.
Luke 22:19 And he took bread, and gave thanks, and brake it, and gave unto them, saying, This is my body which is given for you: this do in remembrance of me.
Luke 22:20 Likewise also the cup after supper, saying, This cup is the new testament in my blood, which is shed for you.
1 Cor. 1:22 For the Jews require a sign, and the Greeks seek after wisdom:
1 Cor. 1:23 But we preach Christ crucified, unto the Jews a stumblingblock, and unto the Greeks foolishness;
1 Cor. 1:24 But unto them which are called, both Jews and Greeks, Christ the power of God, and the wisdom of God.
1 Cor. 1:25 Because the foolishness of God is wiser than men; and the weakness of God is stronger than men.
1 Cor. 1:26 For ye see your calling, brethren, how that not many wise men after the flesh, not many mighty, not many noble, are called:
2 Gal. 3:27; 1 Cor. 10:16-17
For as many of you as have been baptized into Christ have put on Christ.
1 Cor. 10:16 The cup of blessing which we bless, is it not the communion of the blood of Christ? The bread which we break, is it not the communion of the body of Christ?
1 Cor. 10:17 For we being many are one bread, and one body: for we are all partakers of that one bread.
This doctrine across the Standards
Where the Confession and the Westminster Larger Catechism treat the same matter, so the question can be studied alongside its parallel statements.
In the Westminster Confession
VII.6 Under the gospel, when Christ the substance was exhibited, the ordinances in which this covenant is dispensed are …
Under the gospel, when Christ the substance was exhibited, the ordinances in which this covenant is dispensed are the preaching of the Word and the administration of the sacraments of Baptism and the Lord's Supper; which, though fewer in number, and administered with more simplicity and less outward glory, yet in them it is held forth in more fulness, evidence, and spiritual efficacy, to all nations, both Jews and Gentiles; and is called the New Testament. There are not, therefore, two covenants of grace differing in substance, but one and the same under various dispensations.
→ VII.6 · Of God's Covenant with ManXXVII.1 Sacraments are holy signs and seals of the covenant of grace, immediately instituted by God, to represent Christ …
Sacraments are holy signs and seals of the covenant of grace, immediately instituted by God, to represent Christ and his benefits, and to confirm our interest in him: as also to put a visible difference between those that belong unto the Church and the rest of the world; and solemnly to engage them to the service of God in Christ, according to his Word.
→ XXVII.1 · Of the SacramentsXXVII.2 There is in every sacrament a spiritual relation or sacramental union, between the sign and the thing signified; …
There is in every sacrament a spiritual relation or sacramental union, between the sign and the thing signified; whence it comes to pass that the names and the effects of the one are attributed to the other.
→ XXVII.2 · Of the SacramentsXXVII.3 The grace which is exhibited in or by the sacraments, rightly used, is not conferred by any power …
The grace which is exhibited in or by the sacraments, rightly used, is not conferred by any power in them; neither doth the efficacy of a sacrament depend upon the piety or intention of him that doth administer it, but upon the work of the Spirit, and the word of institution, which contains, together with a precept authorizing the use thereof, a promise of benefit to worthy receivers.
→ XXVII.3 · Of the SacramentsXXVII.4 There be only two sacraments ordained by Christ our Lord in the Gospel, that is to say, Baptism …
There be only two sacraments ordained by Christ our Lord in the Gospel, that is to say, Baptism and the Supper of the Lord: neither of which may be dispensed by any but by a minister of the Word lawfully ordained.
→ XXVII.4 · Of the SacramentsXXVII.5 The sacraments of the Old Testament, in regard of the spiritual things thereby signified and exhibited, were, for …
The sacraments of the Old Testament, in regard of the spiritual things thereby signified and exhibited, were, for substance, the same with those of the New.
→ XXVII.5 · Of the SacramentsIn the Westminster Larger Catechism
Q.161 How do the sacraments become effectual means of salvation?
The sacraments become effectual means of salvation, not by any power in themselves, or any virtue derived from the piety or intention of him by whom they are administered, but only by the working of the Holy Ghost, and the blessing of Christ, by whom they are instituted.
→ Open Q.161Q.162 What is a sacrament?
A sacrament is a holy ordinance instituted by Christ in his church, to signify, seal, and exhibit unto those that are within the covenant of grace, the benefits of his mediation; to strengthen and increase their faith, and all other graces; to oblige them to obedience; to testify and cherish their love and communion one with another; and to distinguish them from those that are without.
→ Open Q.162Q.163 What are the parts of a sacrament?
The parts of a sacrament are two; the one an outward and sensible sign, used according to Christ's own appointment; the other an inward and spiritual grace thereby signified.
→ Open Q.163Q.164 How many sacraments hath Christ instituted in his church under the New Testament?
Under the New Testament Christ hath instituted in his church only two sacraments, Baptism and the Lord's supper.
→ Open Q.164