- For Baptism and original. The best answer would be from the Catechism itself. Here is the link for baptism, which also addresses original sin : scborromeo.org/ccc/p2s2c1a1.htm
And original sin also from the catechism: 406 The Church’s teaching on the transmission of original sin was articulated more precisely in the fifth century, especially under the impulse of St. Augustine’s reflections against Pelagianism, and in the sixteenth century, in opposition to the Protestant Reformation. Pelagius held that man could, by the natural power of free will and without the necessary help of God’s grace, lead a morally good life; he thus reduced the influence of Adam’s fault to bad example. The first Protestant reformers, on the contrary, taught that original sin has radically perverted man and destroyed his freedom; they identified the sin inherited by each man with the tendency to evil (concupiscentia), which would be insurmountable. The Church pronounced on the meaning of the data of Revelation on original sin especially at the second Council of Orange (529) and at the Council of Trent (1546).
and God created man in his image and established him in his friendship. A spiritual creature, man can live this friendship only in free submission to God. The prohibition against eating “of the tree of the knowledge of good and evil” spells this out: "for in the day that you eat of it, you shall die."276 The "tree of the knowledge of good and evil"277 symbolically evokes the insurmountable limits that man, being a creature, must freely recognize and respect with trust. Man is dependent on his Creator, and subject to the laws of creation and to the moral norms that govern the use of freedom.
Man’s first sin
397 Man, tempted by the devil, let his trust in his Creator die in his heart and, abusing his freedom, disobeyed God’s command. This is what man’s first sin consisted of.278 All subsequent sin would be disobedience toward God and lack of trust in his goodness.
398 In that sin man preferred himself to God and by that very act scorned him. He chose himself over and against God, against the requirements of his creaturely status and therefore against his own good. Constituted in a state of holiness, man was destined to be fully “divinized” by God in glory. Seduced by the devil, he wanted to “be like God”, but “without God, before God, and not in accordance with God”.279
399 Scripture portrays the tragic consequences of this first disobedience. Adam and Eve immediately lose the grace of original holiness.280 They become afraid of the God of whom they have conceived a distorted image - that of a God jealous of his prerogatives.281
400 The harmony in which they had found themselves, thanks to original justice, is now destroyed: the control of the soul’s spiritual faculties over the body is shattered; the union of man and woman becomes subject to tensions, their relations henceforth marked by lust and domination.282 Harmony with creation is broken: visible creation has become alien and hostile to man.283 Because of man, creation is now subject “to its bondage to decay”.284 Finally, the consequence explicitly foretold for this disobedience will come true: man will “return to the ground”,285 for out of it he was taken. Death makes its entrance into human history.286
401 After that first sin, the world is virtually inundated by sin There is Cain’s murder of his brother Abel and the universal corruption which follows in the wake of sin. Likewise, sin frequently manifests itself in the history of Israel, especially as infidelity to the God of the Covenant and as transgression of the Law of Moses. And even after Christ’s atonement, sin raises its head in countless ways among Christians.287 Scripture and the Church’s Tradition continually recall the presence and universality of sin in man’s history:
What Revelation makes known to us is confirmed by our own experience. For when man looks into his own heart he finds that he is drawn towards what is wrong and sunk in many evils which cannot come from his good creator. Often refusing to acknowledge God as his source, man has also upset the relationship which should link him to his last end, and at the same time he has broken the right order that should reign within himself as well as between himself and other men and all creatures.288