Because of "Kdusha,"(Holiness) and in order to prevent mispronunciation of the four-letter Name (The Essence of the L-RD), Jews usually substitute the Name with a single Hebrew letter or phrase, or as HASHEM, or Adonai. In Traditional Siddurim and Bibles you may find G-d's Essence Name. This is the four-letter Name that starts with the letter "Yood." A True Jew will never say this Name because of "Yir-at HASHEM," or Fear and Deep Devotion of/to G-d.
Exd 3:14 And G-d said unto Moses: 'I AM THAT I AM'; and He said: 'Thus shalt thou say unto the children of Israel: I AM hath sent me unto you.'
Amo 6:10 And a man's uncle shall take him up, and he that burneth him, to bring out the bones out of the house, and shall say unto him that is by the sides of the house, Is there yet any with thee? and he shall say, No. Then shall he say, Hold thy tongue: for we may not make mention of the name of the L-RD.
Jhn 7:28-29 Then cried Y'shua in the temple as he taught, saying, Ye both know me, and ye know whence I am: and I am not come of myself, but He that sent me is true, Whom ye know not.
But I know Him: for I am from Him, and He hath sent me.
Jhn 8:58 Y'shua said unto them, Verily, verily, I say unto you, Before Abraham was, I Am.
Jhn 15:16 Ye have not chosen me, but I have chosen you, and ordained you, that ye should go and bring forth fruit, and that your fruit should remain: that whatsoever ye shall ask of the Father in my name, He may give it you.