Why does Psalm 103:8 use the dual form of אַפַּ֣יִם (anger)?

Question

In Psalm 103:8 we read:

אֶ֖רֶךְ אַפַּ֣יִם וְרַב־חָֽסֶד

Why is אַפַּ֣יִם (anger) in its dual form?

Answer 1

In Psalm 103:8, Why is אַפַּ֣יִם (anger) in its dual form?

When the ‘Anger of YHVH’ is against 1 person (Moshe), it’s in the singular form in Exodus 4:14 ( אַ֨ף יְהֹוָ֜ה ).

In Numbers 12:9 we find ‘Anger of YHVH’ in its singular form ( אַ֧ף יְהֹוָ֛ה ), even though the Anger is against 2 people (Aharon & Miriam).

Even when the ‘Anger of YHVH’ is against 1 land (Egypt) the singular form is used ( אַ֥ף יְהֹוָ֖ה) in Deuteronomy 29:26.

Even when the ‘Anger of YHVH’ is against 1 Nation (Yisrael) the singular form is used ( אַף־יְהֹוָה֙ ) in Joshua 23:16.

Even during David’s reign, the ‘Anger of YHVH’ is singular ( אַ֚ף יְהֹוָה֙ ) against 1 enemy ( Uzzah ) in 2 Samuel 6:7. - Then later against (Yisrael) in 2 Samuel 24:1 the ‘Anger of YHVH’ ( אַף־יְהֹוָ֔ה ) remains singular.

Later in the time of Yeshayahu, the ‘Anger of YHVH’ ( אַף־יְהֹוָ֨ה ) remains singular against His people in Isaiah 5:25.

• At what point does the ‘Anger of YHVH’ become plural?

Perhaps the dual form of Anger (אַפַּ֣יִם) in Psalm 103:8 is create “Parallelism” to the dual form of His Ways (דְּרָכָ֣יו) stated in verse 9.

Answer 2

The plural form used here is a Hebrew idiom that depicts "anger" as "flared nostrils".

( masc., אף / aph ) Translation: NOSE Definition: The organ bearing the nostrils on the anterior of the face. Also meaning anger from the flaring of the nostrils and the redness of the nose when angry. Relationship to Root: The nostrils of man flares when he breathes heavy in passion or anger. Alternate Translations: nostrils (when in the double plural form) KJV Translations: anger, wrath, face, nostrils, nose, angry Strong's Hebrew #: h.0639
-- Ancient Hebrew Lexicon of the Bible

It is mostly used in reference to Yahweh, who is said to have אֶ֖רֶךְ אַפַּ֣יִם "long nostrils", i.e. it takes Him a long time to get angry (KJV: longsuffering/slow to anger), viz:

Num 14:18,
Neh 9:17,
Ps 86:15, 103:8, 145:8,
Prov 14:29, 16:32,
Joel 2:13,
Jonah 4:2,
Nah 1:3

Additional Note

The use of the plural here, and in all the verses listed, emphasizes Yahweh's "long-suffering" nature. In the spirit of the idiom, having two nostrils would enhance Yahweh's capacity to take deep calming breaths as He watched mankind wrestling with the reality of having "the freedom to do as you please".