These are excerpts from an older standard textbook for instructing people preparing for Confirmation:
21 Q. Is there but one God? A. Yes; there is but one God.
22 Q. Why can there be but one God? A. There can be but one God because God, being supreme and infinite, cannot have an equal.
"Supreme," that is, the highest. "Equal," when two are equal one has everything the other has. You could say one pen is the equal of another if it is just as nice and will write just as well; one mechanic is the equal of another if he can do the work equally well. Two boys are equal in class if they have exactly the same marks at the end of the month or year. You could not have two persons chief. For example, you could not have two chief generals in an army; two presidents in the nation, or two governors in a state, or two mayors in a city, or two principals in a school, unless they divide equally their power, and then they will be equals and neither of them chief. God cannot divide His power with anyone—so as to give it away entirely—because we say He is infinite, and that means to have all. Others have only the loan of their power from God. Therefore, all power and authority come from God; so that when we disobey our parents or superiors who are placed over us, we disobey God Himself.
23 Q. How many persons are there in God? A. In God there are three divine persons really distinct and equal in all things—the Father, the Son, and the Holy Ghost.
"Distinct," not mingled together. We call the first and second persons Father and Son, because the second is begotten by the first person, and not to indicate that there is any difference in their age. We always see in the world that a father is older than his son, so we get the idea perhaps that it is the same in the Holy Trinity. But it is not so. God the Father, and God the Son, and God the Holy Ghost existed from all eternity, and one did not exist before the other. God the Son is just as old as God the Father, and this is another great mystery. Even in nature we see that two things may begin to exist at the same time, and yet one be the cause of the other. You know that fire is the cause of heat; and yet the heat and the fire begin at the same time. Though we cannot understand this mystery of the Father and Son, we must believe it on the authority of God, who teaches it. First, second, and third person in the Blessed Trinity does not mean, therefore, that one person was before the other, or brought into existence by the other.
24 Q. Is the Father God? A. The Father is God and the first Person of the Blessed Trinity.
25 Q. Is the Son God? A. The Son is God and the second Person of the Blessed Trinity.
26 Q. Is the Holy Ghost God? A. The Holy Ghost is God and the third Person of the Blessed Trinity.
27 Q. What do you mean by the Blessed Trinity? A. By the Blessed Trinity I mean one God in three Divine Persons.
*28 Q. Are the three Divine Persons equal in all things? A. The three Divine Persons are equal in all things.
29 Q. Are the three Divine Persons one and the same God? A. The three Divine Persons are one and the same God, having one and the same divine nature and substance.
Though they are one and the same, we sometimes attribute different works to them. For example, works of creation we attribute to God the Father; works of mercy to God the Son; and works of love and sanctification to the Holy Ghost; and you will often find them thus spoken of in pious books; but all such works are done by all the Persons of the Trinity; because such works are the works of God, and there is but one God.
*30 Q. Can we fully understand how the three Divine Persons are one and the same God? A. We cannot fully understand how the three Divine Persons are one and the same God, because this is a mystery.
"Fully"—entirely. We can partly understand it. We know what one God is and we know what three persons are; but how these two things go together is the part we do not understand—the mystery.
*31 Q. What is a mystery? A. A mystery is a truth which we cannot fully understand.
"A truth," that is, a revealed truth—one made known to us by God or His Church. It is a truth which we must believe though we cannot understand it. Let us take an example. When a boy goes to school he is taught that the earth is round like an orange and revolving in two ways, one causing day and night and the other producing the seasons: spring, summer, autumn, winter. The boy goes out into the country where he sees miles of level land and mountains thousands of feet in height. Again he goes out on the ocean where sailors tell him it is several miles in depth.
Now he may say: how can the earth be round if deep valleys, high mountains, and level plains prove to my senses the very opposite, and the countless things at rest upon its surface tell me it is motionless. Yet he believes even against the testimony of his senses that the earth is round and moving, because his teacher could have no motive in deceiving him; knows better than he, having learned more, and besides has been taught by others who after long years of careful study and research have discovered these things and know them to be true. If therefore we have to believe things that we do not understand on the authority of men, why should we not believe other truths on the authority of God? Yes, we must believe Him. If a boy knew all his teacher knew there would be no need of his going to school; he would be the equal in knowledge of his teacher, and if we knew all that God knows we would be as great as He. As well might we try to empty the whole ocean into the tiny holes that children dig in the sand by its shore, as fully to comprehend the wisdom of God. This is the mistake unbelievers make when they wish to understand with their limited intelligence the boundless knowledge and mysterious ways of God, and when they cannot understand refuse to believe. Are they not extremely foolish? Would you not ridicule the boy who refuses to believe that the earth is round and moving because he cannot understand it? As he grows older and learns more he will comprehend it better; so we, when we leave this world and come into the presence of God, shall see clearly many things that are unintelligible now. For the present, we have only to believe them on the authority of God teaching us. Another example. We take two little black seeds that look just alike and place them in the same kind of soil; we put the same kind of water upon them; they have the same sunlight and air, and yet when they grow up one has a red flower and one a blue. Where did the red and where did the blue come from? From the black seed, or the brown soil, or the pure water, air and sunlight? We do not know. It is there, and that is all. We see it and believe it, though we do not understand it.
So if we refuse to believe everything we do not understand, we shall soon believe very little and make ourselves ridiculous.
61 Q. Who is the Redeemer? A. Our Blessed Lord and Saviour Jesus Christ is the Redeemer of mankind.
62 Q. What do you believe of Jesus Christ? A. I believe that Jesus Christ is the Son of God, the second Person of the Blessed Trinity, true God and true man.
"True God." He was true God equal to His Father from all eternity. He became man when He came upon the earth about 2,000 years ago, and was born on Christmas Day. Now He is in Heaven as God and man. Therefore, He was God always, but man only from the time of His Incarnation.
*63 Q. Why is Jesus Christ true God? A. Jesus Christ is true God because He is the true and only Son of God the Father.
God the Father, first Person of the Blessed Trinity, is His real Father, and St. Joseph was His foster-father, selected by the Heavenly Father to take care of Our Lord and watch over Him while on earth. A foster-father is not the same as a stepfather. A stepfather is a second father that one gets when his real father dies. A foster-father is one who takes a person, whether a relative or a stranger, and adopts him as his son. It was a very great honor for St. Joseph to be selected from among all men to take care of the Son of God; to carry in his arms the great One of whom the prophets spoke; the One for whom the whole world longed during so many thousand years; so that next to our Blessed Mother St. Joseph deserves our greatest honor.
*64 Q. Why is Jesus Christ true man? A. Jesus Christ is true man because He is the Son of the Blessed Virgin Mary, and has a body and soul like ours.
He has all that we have by nature, but not the things we have acquired such as deformities, imperfections, and the like. Everything in Our Lord was perfect. Above all, He had no sin of any kind; nor even inclination to sin. He could be hungry, as He was when He fasted forty days in the desert. (Matt. 4:2). He was thirsty, as He said on the Cross. (John 19:28). He could be wearied; as we read in the Holy Scripture (John 4:6) that He sat down by a well to rest, while His disciples went into the city to buy food. All these sufferings come from our very nature. We say a thing comes from our very nature when everybody has it. Now, everyone in the world may at times be hungry, thirsty, or tired; but everybody in the world need not have a toothache or headache, because such things are not common to human nature, but due to some defect in our body; and such defects Our Lord did not have, because He was a perfect man. Therefore, Our Lord had a body like ours, not as it usually is with defects, but as it should be, perfect in all things that belong to its nature, as Adam's was before he sinned.
*65 Q. How many natures are there in Jesus Christ? A. In Jesus Christ there are two natures: the nature of God and the nature of man.
He was perfect God and perfect man. His human nature was under the full power of His divine nature, and could not do anything contrary to His divine will. You cannot understand how there can be two natures and two wills in one person, because it is another of the great mysteries; but you must believe it, just as you believe there are three Persons in one God, though you do not understand it. Those who learn theology and study a great deal may understand it better than you, but never fully. It will be enough, therefore, for you to remember and believe that there are two natures—the divine nature and the human nature—in the one person of Our Lord.
*66 Q. Is Jesus Christ more than one person? A. No, Jesus Christ is but one Divine Person.
"But one," so that the Second Person of the Blessed Trinity, the Son of God, the Messias, Christ, Jesus, Our Lord, Our Saviour, Our Redeemer, etc., are all names for the one Person; and, besides these, there are many other names given to Our Lord in the Holy Scripture, both in the Old and the New Testaments.
*67 Q. Was Jesus Christ always God? A. Jesus Christ was always God, as He is the Second Person of the Blessed Trinity, equal to His Father from all eternity.
*68 Q. Was Jesus Christ always man? A. Jesus Christ was not always man, but became man at the time of His Incarnation.
69 Q. What do you mean by the Incarnation? A. By the Incarnation I mean that the Son of God was made man.
70 Q. How was the Son of God made man? A. The Son of God was conceived and made man by the power of the Holy Ghost, in the womb of the Blessed Virgin Mary.
*71 Q. Is the Blessed Virgin Mary truly the Mother of God?
A. The Blessed Virgin Mary is truly the Mother of God, because the same
Divine Person who is the Son of God is also the Son of the Blessed