The Torah's double command — Devarim 5:16 ordaining honor and Yevamot 5b–6a citing the baraita that one might have thought honor of parents overrides Shabbat — establishes that the duty is of the highest biblical gravity, while the baraita itself clarifies that God's command still supersedes a parent's instruction, as Rashi on Vayikra 19:3 puts it: both the child and the parent are obligated in God's honor, so one may not heed a parent's word to violate Torah.
The Gemara in Kiddushin 30b draws the foundational equation: just as Scripture uses 'honor' for God and for parents, and 'fear' for God and for parents, the duty owed to one's father and mother is Divinely calibrated — a principle echoed by Kitzur Shulchan Arukh 143:1, Sifra, Kedoshim, Section 1:5, Tur, Yoreh De'ah 240, and Levush, Yoreh De'ah 240:1, all of which ground the obligation's intensity in this explicit scriptural equation.
The positive content of honor is defined in consistent terms across the sources: feeding, giving drink, dressing, covering, bringing in, and taking out one's parents — as stated by Sefer HaMitzvot, Positive Commandments 210, Sefer HaChinukh 33:1, Rashi on Vayikra 19:3, Shulchan Arukh, Yoreh De'ah 240:1, Chayyei Adam 67:4, and Arukh HaShulchan, Yoreh De'ah 240:16 — and crucially, the Shulchan Arukh adds that even feeding a parent the finest food while showing an angry face incurs punishment, while grinding a parent at a millstone with genuinely good intent and gentle words earns a share in the World to Come.
The content of fear (mora) is equally precise: Mishneh Torah, Rebels 6:1–13 enumerates that one must not stand or sit in the parent's designated place, not contradict or outweigh their words, and not call them by name — living or dead; Sefer HaChinukh 212:1 and Arukh HaShulchan, Yoreh De'ah 240:16 extend this to the extreme case in which a parent, before an assembled public, tears a child's fine garments, strikes his head, and spits in his face — and the child must remain silent rather than shame them, seeing himself as standing before the King of kings who so commanded.
The measure of the duty is illustrated by the story of Dama ben Netina, cited in Kiddushin 31a by both Rav Ulla and Rabbi Eliezer: a gentile who refused to disturb his sleeping father even at the cost of six hundred thousand gold dinars' profit — and Rabbi Eliezer in Kiddushin 32a adds that the duty extends even to a case where the father seizes a purse and throws it into the sea, and the son does not embarrass him, which Sdei Chemed, Maarechet Kaf 144 identifies as the standard debated by the Rif and Rambam regarding the distinction between lack of honor and active humiliation.
Sefer HaChinukh 33:1 gives the philosophical root: a person must acknowledge and repay kindness to those who benefited him, and since parents are the cause of his very existence in the world, gratitude to them is both morally compelling and utterly fitting — a rationale supplemented by מכתב מאליהו, חלק ה עמוד תכא, which notes that recognition of goodness is the primary reason for this mitzva and that the honor of parents also serves the social order by which parents raise children and children sustain parents in old age.
Father and mother are equal in both honor and fear in principle — Keritot 28a and Sifra, Kedoshim, Section 1:5 derive this from the reversal of order between the two verses — yet the Sages rule that the father takes precedence in practice everywhere because both the child and the mother are themselves obligated in the father's honor; when there is a conflict in practice, Shulchan Arukh, Yoreh De'ah 240:14 and Levush, Yoreh De'ah 240:14 rule that the child sets aside the mother's request to attend to the father's, unless the mother is divorced, in which case both are equal.
The duty is not absolute when it conflicts with other mitzvot: Levush, Yoreh De'ah 240:15 rules that if a parent orders a child to violate any Torah commandment — positive, negative, or rabbinic — the child must not obey, since all are obligated in God's honor, whose fear supersedes theirs; and Kiddushin 32a records the view of Elazar ben Matya that when a mitzva cannot be performed by others, it takes precedence over honoring the father, while Issi ben Yehuda counsels delegating the mitzva to others wherever possible so as to keep fulfilling one's duty to the parent, a balance codified by Shulchan Arukh, Yoreh De'ah 240:12 and by Mishneh Torah, Rebels 6:13, which adds that Torah study is greater than honor of father and mother.
The obligation falls even upon a child whose parent is wicked: Shulchan Arukh, Yoreh De'ah 240:18 rules that even a mamzer is obligated in the honor and fear of a father who is sinful and transgresses, though the Rema records a dissenting opinion that one need not honor a wicked parent who has not repented.
The Sefer Charedim Sefer Charedim, Positive Commandments 6:2 adds the branch of rising fully to one's feet upon a parent's approach — even a hundred times a day according to the Mordechai — and extends this obligation of rising to grandparents and step-parents; Mishneh Torah, Torah Study 5:1 places honor of one's teacher above even honor of one's father, since the father brings one into this world while the teacher who imparts wisdom brings one to the World to Come.
The financial dimension of the obligation is addressed by Bach, Yoreh De'ah 240, which records the positions of the Rif, Rambam, and others that when a parent has no means, the court compels the child to support him — but only up to the measure of what the child is obligated to give to charity proportional to his wealth, not all his assets, though the Semag and Semak hold that the obligation to support a destitute parent flows from the law of honor itself and may even require hiring oneself out on the parent's behalf; Sdei Chemed, Maarechet Kaf 147 further discusses the ruling of Maharik, codified by the Rema, that a parent who objects to a child's chosen marriage partner need not always be obeyed.