In the wilderness, Moses wards off an attack by poisonous serpents on the children of Israel, by using the power of suggestion to mitigate the impact of their fear of being bitten, fear more deadly than the poisonous bite itself. The bronze image of a serpent raised above the people will rescue them if they will keep looking at it.
'And if anyone was bitten by a serpent, he looked at the bronze serpent and lived.' (Num 21:9)
It's an image Jesus draws upon in cryptic reference to his own fate, being lifted up on the cross, first in his night time conversation with Nicodemus
"And just as Moses lifted up the serpent in the wilderness, so must the Son of Man be lifted up." (John 3:14)
Later, in conversation with his critics among the Pharisees he alludes to his death again with the same cryptic image, suggesting it is the point of reference for revealing who he is
"When you have lifted up the Son of Man, then you will realise that I am he, and that I do nothing on my own, but I speak these things as my Father has instructed me." (John 8:28)
And, he says it again in the Temple to the disciples, when some Greeks have asked to speak with him
"Now judgement is upon this world; now the ruler of this world will be cast out. And I, if I am lifted up from the earth, will draw all men to myself." (John 12:31-2)
John the evangelist explicitly states that 'lifted up' refers to his execution.
'But he was saying this to indicate the kind of death by which he was to die.' (John 12:33)
The cross is not yet mentioned, but John prepares those hearing the Passion story to look straight at his coming death, and find in it an image of healing and rescue.
When the method of his execution is revealed, it comes as a shock, a traumatic event that affects all who witness it. Death by crucifixion was regarded as a shameful curse, not only on the person but all associated with them, something nobody could live down.
Paradoxically, this worst possible scenario, confronted in earnest, will reveal the immensity of divine love and mercy for all humankind. This gives meaning to the phrase 'Look and live'. Thus the act of gazing on any image of the crucified one, or the cross itself, no matter how elaborate or simple it may be, no matter how realistic or abstract it may be, becomes a path to prayer and communion with God.
'When I survey the wondrous cross on which the prince of glory died,
me riches gain I count but loss, and pour contempt on all my pride.'
'Love so amazing, so divine, demands my soul my life my all.'