Lewis is glossing quickly over some pretty heavy theological concepts here. In general he is discussing what some groups would call the sacraments and others would refer to as ordinances. Belief (or faith), of course, is neither a sacrament nor an ordinance but is a foundational element of all Christian creeds. (Hebrews 11:6: "But without faith it is impossible to please him: for he that cometh to God must believe that he is, and that he is a rewarder of them that diligently seek him.")
The term "sacrament" may be defined as "an outward sign combined with a prescribed form of words and regarded as conferring some specific grace upon those who receive it. The Protestant sacraments are baptism and the Lord's Supper. In the Roman Catholic and Eastern Churches they are baptism, penance, confirmation, the Eucharist, holy orders, matrimony, and the anointing of the sick (formerly extreme unction)" (Collins English Dictionary). However, some Protestant groups (e.g., Baptists) are uncomfortable with the term "sacrament" and prefer instead the word "ordinance."
"The Catechism of the Catholic Church defines the sacraments as 'efficacious signs of grace, instituted by Christ and entrusted to the Church, by which divine life is dispensed to us. The visible rites by which the sacraments are celebrated signify and make present the graces proper to each sacrament. They bear fruit in those who receive them with the required dispositions.' The catechism included in the Anglican Book of Common Prayer defines a sacrament as "an outward and visible sign of an inward and spiritual grace given unto us, ordained by Christ himself, as a means whereby we receive the same, and a pledge to assure us thereof.
"Some Protestant traditions avoid the word 'sacrament'. . . . Baptists . . . prefer instead the word 'ordinance', practices ordained by Christ to be permanently observed by the church." (wikipedia; emphasis added).
Some Christian groups consider baptism as necessary for salvation; some consider it a symbolic ritual that follows salvation. Modes of baptism vary among different denominations; it generally involves immersion, sprinkling, or pouring water on the individual. Some groups baptize infants; others baptize only those who have made a profession of faith in Christ.
Holy Communion, the Mass, the Lord's Supper
Matthew 26:26-28 (King James Version): "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. And he took the cup, and gave thanks, and gave it to them, saying, Drink ye all of it; For this is my blood of the new testament, which is shed for many for the remission of sins." (See also Mark 14 and Luke 22.)
1 Corinthians 11:23-29 (King James Version): "For I have received of the Lord that which also I delivered unto you, That the Lord Jesus the same night in which he was betrayed took bread: And when he had given thanks, he brake it, and said, Take, eat: this is my body, which is broken for you: this do in remembrance of me. After the same manner also he took the cup, when he had supped, saying, This cup is the new testament in my blood: this do ye, as oft as ye drink it, in remembrance of me. For as often as ye eat this bread, and drink this cup, ye do shew the Lord's death till he come. Wherefore whosoever shall eat this bread, and drink this cup of the Lord, unworthily, shall be guilty of the body and blood of the Lord. But let a man examine himself, and so let him eat of that bread, and drink of that cup. For he that eateth and drinketh unworthily, eateth and drinketh damnation to himself, not discerning the Lord's body."
As with baptism, various denominations practice Communion in differing ways. All use wine (some substitute nonalcoholic grape juice) and bread to represent Christ's blood and body.