Kabbalistic Use
One of the most important names is that of the Ein Sof (אין סוף "Void", "Infinite" or "Endless"). The forty-two-lettered name contains the combined names אהיה יהוה אדוני הויה, that when spelled out contains 42 letters. The equivalent in value of YHWH (spelled הא יוד הא וו = 45) is the forty-five-lettered name.
The seventy-two-lettered name is derived from three verses in Exodus (14:19–21) beginning with "Vayyissa", "Vayyabo" and "Vayyet" respectively. Each of the verses contains 72 letters, and when combined they form 72 names, known collectively as the Shemhamphorasch. The kabbalistic book Sefer Yetzirah explains that the creation of the world was achieved by the manipulation of these sacred letters that form the names of God.
Read more about this topic: Names Of God In Judaism