2 i dont know what any of that was doing in an answer. if you dont understand a question, comment asking for clarification.
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I agree with @Scimonster's comment, above, as there are two groups. It is also unclear since you combined Yahrtzeit candles (in your question title) with asking about Yom Tov, whether you imply why we have Yizkor on Yom Tov, which, in turn explains why we light a yahrtzeit / Yizkor candle on those days.

At any rate, theThe reason for the yahrtzeit candle comes from the metaphor in

Proverbs 20:27:

נֵ֣ר יְ֭הוָה נִשְׁמַ֣ת אָדָ֑ם חֹ֝פֵ֗שׂ כָּל־חַדְרֵי־בָֽטֶן׃

The spirit of man is the lamp of the LORD, Searching all the inward parts.

Proverbs 20:27:

נֵ֣ר יְ֭הוָה נִשְׁמַ֣ת אָדָ֑ם חֹ֝פֵ֗שׂ כָּל־חַדְרֵי־בָֽטֶן׃

The spirit of man is the lamp of the LORD, Searching all the inward parts.

I agree with @Scimonster's comment, above, as there are two groups. It is also unclear since you combined Yahrtzeit candles (in your question title) with asking about Yom Tov, whether you imply why we have Yizkor on Yom Tov, which, in turn explains why we light a yahrtzeit / Yizkor candle on those days.

At any rate, the reason for the yahrtzeit candle comes from the metaphor in

Proverbs 20:27:

נֵ֣ר יְ֭הוָה נִשְׁמַ֣ת אָדָ֑ם חֹ֝פֵ֗שׂ כָּל־חַדְרֵי־בָֽטֶן׃

The spirit of man is the lamp of the LORD, Searching all the inward parts.

The reason for the yahrtzeit candle comes from the metaphor in

Proverbs 20:27:

נֵ֣ר יְ֭הוָה נִשְׁמַ֣ת אָדָ֑ם חֹ֝פֵ֗שׂ כָּל־חַדְרֵי־בָֽטֶן׃

The spirit of man is the lamp of the LORD, Searching all the inward parts.

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source | link

I agree with @Scimonster's comment, above, as there are two groups. It is also unclear since you combined Yahrtzeit candles (in your question title) with asking about Yom Tov, whether you imply why we have Yizkor on Yom Tov, which, in turn explains why we light a yahrtzeit / Yizkor candle on those days.

At any rate, the reason for the yahrtzeit candle comes from the metaphor in

Proverbs 20:27:

נֵ֣ר יְ֭הוָה נִשְׁמַ֣ת אָדָ֑ם חֹ֝פֵ֗שׂ כָּל־חַדְרֵי־בָֽטֶן׃

The spirit of man is the lamp of the LORD, Searching all the inward parts.