Ahavah means “love” in Hebrew. The Jewish mystics remark on the affinity between the word ahavah, “love,” and “echad,” one. The numerical value of their letters is the same: 13.
Oneness, unity, is the aspiration of love, and love emerges from a perception of unity.
This is what is meant by, “You are to know this day and take into your heart that HaShem is the Only G-D, in Heaven and On Earth.” The realization that the Law which governs the Universe is AHAVAH which emanates from, permeates and fills all things.
This insight is also expressed in the Shema: שְׁמַע, יִשְׂרָאֵל: יְהוָה אֱלֹהֵינוּ, יְהוָה אֶחָד.
its first line declares God’s unity, and ends with the word “echad.” Then follows the mitzvah to love God. Love comes out of a sense of God’s unity pervading all things.
There are three commands to love in the Torah; First, “You shall love the Lord your God for all your heart, soul and strength” (Deuteronomy 6:4); second, “love your neighbour as yourself” (Leviticus 19:18); and, third, “love the stranger as yourself” (Leviticus 19:34).
The first letter of Ahavah, the Aleph is constructed of “two yuds and a straight nun!” That is, the Nun Sofit! This is to teach that HaShem is the Same, Eternal Kindness [Shmoth 3.15 ] (Echad, Oneness which also begins with the letter Aleph,) Desires Yichud Oneness, which is expressed by the Torah’s phrase, “at the mouth [‘singular’] of two witnesses, that is, their marital testimony must agree to the Ahavah) that HaShem is the Same, Constant One Who, “In the Kingdom – As Above, So Also in the Kingdom Below” Continually Forgives and Supports the Fallen; as it says, “The L-RD upholdeth all that fall, and raiseth up all those that are bowed down.” Tehillim 145.14
Yichud describes the unification, or becoming one, of two bodies or souls. Echad describes what is CONSTANT, UNCHANGING, Eternally the Same! “I have Loved you with an Everlasting Love!!” Jeremiah 31.3
Yichud is thus the process of “bringing back together” the two lost halves of what was initially a single entity.
Zechariah 14.9 And the L-RD shall be King over all the earth; in that day shall the L-RD be One, and His name one.
It might best be expressed in the words of Melech Shlomo (King Solomon): “Thy Love is better than wine.” יִשָּׁקֵנִי מִנְּשִׁיקוֹת פִּיהוּ, כִּי-טוֹבִים דֹּדֶיךָ מִיָּיִן.