The Hebrews did not "convert" letters into numbers. Each of the 22 letters of the alphabet is assigned a number, so that a number is a sequence of letters, regardless of the order they are placed. This makes calculation impossible, as with Roman the numeral system.
It took until the recent Middle Ages before the current numbering system and consequent mathematics was introduced into Europe from North Africa (name of the guy responsible is on the tip of my brain but refuses to emerge from the depths). European science (especially astronomical calculations and observations) was dragged from mythology into genuine enquiry through its contact with the scientists and mathematicians of the Islamic world.
But getting back to the Hebrews and their fascination between numbers and words - search for: Gematria.
Many Jews were/are similarly interested in the esoteric. Search for Kabbalah and Kabbalistic.
Doug