Shemot 15:2 and 3 say:
ב עָזִּי וְזִמְרָת יָהּ, וַיְהִי-לִי {ר} לִישׁוּעָה; {ס} זֶה אֵלִי וְאַנְוֵהוּ, {ס} אֱלֹהֵי {ר} אָבִי וַאֲרֹמְמֶנְהוּ. {ס}
ג יְהוָה, אִישׁ מִלְחָמָה; יְהוָה, {ר} שְׁמוֹ. {ס
Why is God called יָהּ in Shir Ha-Yam, Shemot 15:2, but in 15:3b, the second part of the very next verse, the song says, 'His name is [יְהוָה],' and in 15:1, that is the name used, and so elsewhere in the song (verses 3a, 6 [twice], 11, 16, 17 [twice], 18)?1
Three things surprise us about this abbreviated name, yes, four:
(1) It has not been mentioned before (see Shemot 3:14,15; 6:3).
(2) It is used in the Torah but once more (Shemot 17:16).
(3) It precedes, as observed, the very next line, which says, 'His name is יְהוָה.'
(4) It has the form of a nickname.2
The same phenomenon, the use of יָהּ and יְהוָה, occurs in the poem of Chizqiyyahu (Yeshayahu 38:10-20).
In Shemot 17:16, יָהּ and יְהוָה occur in the same sentence in the oath against Amalek (וַיֹּאמֶר, כִּי-יָד עַל-כֵּס יָהּ, מִלְחָמָה לַיהוָה, בַּעֲמָלֵק--מִדֹּר, דֹּר), so also later in T'hillim 89:9a (יְהוָה, אֱלֹהֵי צְבָאוֹת--מִי-כָמוֹךָ חֲסִין יָהּ)
And in Yeshayahu 12:2 and 26:4 God is uniquely called יָהּ יְהוָה (read from left to right):
הִנֵּה אֵל יְשׁוּעָתִי אֶבְטַח, וְלֹא אֶפְחָד: כִּי-עָזִּי וְזִמְרָת יָהּ יְהוָה, וַיְהִי-לִי לִישׁוּעָה.
בִּטְחוּ בַיהוָה, עֲדֵי-עַד: כִּי בְּיָהּ יְהוָה, צוּר עוֹלָמִים
It curiously alternates with Yahu as the ending of personal names, as in Eliyah/Eliyahu, Yeshayah/Yeshayahu, Yirm'yah/Yirm'yahu.
1 The New Jewish Publication Society Version (NJPSV) transcribes Yah in 15:2 as the LORD to make this form of God's name consistent with the ten uses of Yhvh used elsewhere in the song and transcribed by the translators in English as the LORD. In this way, the difficulty posed by the two forms is eliminated. (Only in Yeshayahu 12:2, 26:4, and 38:11 (twice) is Yah transcribed in this version in the main text, and in a footnote at Shemot 15:2, though it occurs nineteen times in Psalms, excluding the twenty-four occurrences in the exclamatory HALLELUYAH [NJPSV traditionally transcribes this as Hallelujah, Yah being spelled with a 'small j,' which is customarily pronounced by everyone as a 'y'].
2 In all languages, a shortened form of someone's name is called a nickname and conveys informality (for example, Josh is the nickname of Joshua). But the conveyance of informality with respect to God is incongruous with the fact that he is called in the other verses of the song Yhvh and the fact that this is a song which was sung in worship at the Sea of Reeds.
