Chapter 26, Verse 42

Missing Vav in  “Eliyahu”

 וְזָֽכַרְתִּ֖י אֶת־בְּרִיתִ֣י יַֽעֲק֑וֹב וְאַף֩ אֶת־בְּרִיתִ֨י יִצְחָ֜ק וְאַ֨ף אֶת־בְּרִיתִ֧י אַבְרָהָ֛ם אֶזְכֹּ֖ר וְהָאָ֥רֶץ אֶזְכֹּֽר

Then will I remember my covenant with Jacob, and also my covenant with Isaac, and also my covenant with Abraham will I remember; and I will remember the land.

Rashi

In only five places*in Scripture the name יעקוב is written in full (i.e. with a Vav) ,
and only in five places** the name אליהו is written with the vav missing from his
name i.e. אליה .

Jacob took the letter “vav”from the name of אליהו the prophet as security-that he (Eliyahu) will come and herald the redemption of his (Jacob’s) children, speedily in our days. The
five instances of the Vav symbolize the five fingers of the hand i.e. this
security arrangement between Jacob and Elijah was sealed with a
handshake.(GurAryeh)

*The five places with the full name of יעקוב are as follows:
Vayikra Ch. 26 v.42
Jeremiah Ch. 30 v.18
Jeremiah Ch. 33 v.26
Jeremiah Ch. 46 v.27
Jeremiah Ch. 59 v.19

**The five places of Eliyahu without the Vav are as follows:
2 Kings Ch.1 v. 3
2 Kings Ch.1 v. 4
2 Kings Ch.1 v. 8
2 Kings Ch.1 v. 12
2 Kings Ch.3 v. 27