John 3: verses 14 - 16
14 And as Moses lifted up the serpent in the wilderness, even so must the Son of man be lifted up: 15 That whosoever believeth in him should not perish, but have eternal life. 16 For God so loved the world, that he gave his only begotten Son, that whosoever believeth in him should not perish, but have everlasting life.
Even as Moses was commanded by GOD to form a brazen serpent around a pole and raise it up so that if anyone looked to it believing, they would not die from the snake bite.
THAT was an IMAGE of CHRIST being lifted up off the earth on a Roman cross so that whosoever shall call upon HIM and ask forgiveness shall be saved....