Since, then, faith alone makes us share In Christ and all His benefits, where does such faith originate?

The Holy Spirit creates it in our hearts by the preaching of the holy gospel, and confirms it by the use of the holy sacraments.

What are the Sacraments?

They are visible, holy signs and seals instituted by God in order that by their use He may the more fully disclose and seal to us the promise of the gospel, namely, that because of the one sacrifice of Christ accomplished on the cross He graciously grants us the forgiveness of sins and eternal life.

Are both the Word and the Sacraments designed to direct our faith to the one sacrifice of Jesus Christ on the cross as the only ground of our salvation?

Yes, Indeed, for the Holy Spirit teaches in the gospel and confirms by the holy sacraments that our whole salvation is rooted in the one sacrifice of Christ offered for us on the cross.

How many sacraments has Christ Instituted in the New Testament?

Two, holy Baptism and the holy Supper.

I. Faith Originates in the Gospel and Sacraments Serve To Confirm Faith  

A. Salvation is always and exclusively by grace. For by grace are ye saved through faith; and that not of yourselves: it is the gift of God: (Ephesians 2:8)

B. The new birth which marks the new life is something granted from God, not something accomplished by the believer. Jesus answered, Verily, verily, I say unto thee, Except a man be born of water and of the Spirit, he cannot enter into the kingdom of God. (John 3:5 )

Sacraments which claim to accomplish what Scripture
teaches Christ alone accomplishes subtract from the true
gospel and damage the souls of those who use them.

C. The word of God is the instrument of the new birth. Being born again, not of corruptible seed, but of incorruptible, by the word of God, which liveth and abideth for ever. (1 Peter 1:23)

D. The Presbyterian doctrine of God speaking in Scripture extends to all of our teaching about sacraments -WESTMINSTER CONFESSION OF FAITH 1:10 teaches: The supreme Judge, by which all controversies of religion are to be determined, and all decrees of councils, opinions of ancient writers, doctrines of men, and private spirits, are to be examined, and in whose sentence we are to rest, can be no other but the Holy Spirit speaking in the scripture. Jesus answered and said unto them, Ye do err, not knowing the scriptures, nor the power of God. (Matthew 22:29)

E. Genuine PREACHING is a process of bringing the BIBLE INTO THE LIVES OF BELIEVERS. But the word of the Lord endureth for ever. And this is the word which by the gospel is preached unto you. (1 Peter 1:25)

F. In His concluding instructions to the Church, Jesus made baptism an element of the Christian TEACHING MINISTRY. Go ye therefore, and teach all nations, baptizing them in the name of the Father, and of the Son, and of the Holy Ghost:: Teaching them to observe all things whatsoever I have commanded you: and, lo, I am with you alway, even unto the end of the world. Amen. (Matthew 28:19-20)

Authors use alphabets to make words and communicate ideas - not simply because they don't know enough doodles to fill the pages of their books.            

II. God Picks His Sacraments

A. God gave circumcision as a seal of grace and it is the original sacrament. And he received the sign of circumcision, a seal of the righteousness of the faith which he had yet being uncircumcised: that he might be the father of all them that believe, though they be not circumcised; that righteousness might be imputed unto them also: (Romans 4:11)

B. Circumcision was always about grace rather than external forms. And the LORD thy God will circumcise thine heart, and the heart of thy seed, to love the LORD thy God with all thine heart, and with all thy soul, that thou mayest live. (Deuteronomy 30:6)

Doctrines about sacraments which concentrate on external form rather than on internal divine operation miss the original Biblical purpose.

C. The stated purpose of the sacraments is confirmation of something which God accomplishes - the definition does not extend to something which either Repentance or its corollary itself accomplishes. Then Peter said unto them, Repent, and be baptized every one of you in the name of Jesus Christ for the remission of sins, and ye shall receive the gift of the Holy Ghost. (Acts 2:38)

Faith, repentance, and even the Church [in which one publicly
testifies of confidence in God] are all first gifts from God.

D. Baptism focuses on turning to God for what we cannot accomplish. And now why tarriest thou? arise, and be baptized, and wash away thy sins, calling on the name of the Lord. (Acts 22:16)