The letter Y represents an intermediate between the celestial and the spiritual in man, especially in the heavens. Historically, it is closely connected to I and J in English, particularly when it's the initial letter in a word. When it's made with curves, a letter has something of the celestial in it. (Spiritual Experiences 5620, Doctrine Regarding Sacred Scripture 90)

90. Because we are dealing here with the Divinity and holiness of the Word, to what we have already said let me add a relevant narrative account.

I was once sent a little piece of paper from heaven with Hebrew letters on it, but letters written as they were among the ancient people. Today the letters are to some extent formed with straight lines, but among the most ancient peoples they were then rounded and had little hornlike strokes projecting upward. Angels who were with me then said they knew whole meanings from the letters alone, and that they knew the meanings chiefly from the curves of the lines and points of a letter. They then explained what some letters signified separately, and what in combination, saying that he (h), which was added to the names of Abram and Sarai, symbolized infinity and eternity.

The angels explained for me, moreover, the meaning of the Word in Psalms 32:2 from just the letters or syllables alone, the gist of their meaning being that the Lord is merciful also to those who do evil.

[2] They informed me that writing in the third heaven consists of no straight letters, but of letters variously curved, each of which has a meaning, and that the vowel points there serve to indicate the part of the pronunciation which corresponds to affection; that in that heaven they cannot pronounce the vowels i and e, but instead say y or eu; and they do use the vowels a, o, and u, because these vowels have a full sound. They also said they do not pronounce any of the consonants as hard, but as soft. This, they said, is the reason some Hebrew letters have a dot placed within them, to indicate [that they are pronounced as hard, but without a dot] that they are pronounced with a soft sound, saying that hardness in consonants is employed in the spiritual heaven, because there they are concerned with truths, and truth is capable of hardness, unlike the goodness that prompts angels of the celestial kingdom or third heaven.

They said, too, that the Word they have is written with curved letters having symbolic little hornlike projections and points.

It was apparent from this what is meant by the Lord’s saying, “Not one jot or one tittle will pass from the law till all is fulfilled, ” (Matthew 5:18). And, “It is easier for heaven and earth to pass away than for one point of the law to fail” (Luke 16:17).