Mr Justice Mitchell said Joseph Roche, 24, was 'thoroughly dangerous' and 'someone from whom the public must be protected'.
Roche, of Chipperfield, Hertfordshire, was convicted of attempted murder and indecent assault after a trial at Luton Crown Court in May, but sentence was postponed for medical reports.
The trial was told that he shouted 'let your Jesus save you now' as he attacked Linda Hardy, 44, also of Chipperfield, in May last year. He beat her so severely that her face was barely recognisable.
After the jury's verdicts, Mrs Hardy, a devout Christian, said she had forgiven Roche and was praying for him and his family.
She said: 'I have to follow the Lord's example when he said 'Father forgive them'. I believe it was my faith that saved me that day and I have never lost my faith. If anything it has made me stronger. I do not want retribution, I want him to receive some help.'
The judge told Roche that he was likely to repeat his attacks with 'potentially fatal consequences for your victim'.
Mrs Hardy, a mother-of-two, was walking her dogs on Chipperfield Common in May last year and stopped to sit by a beauty spot called Apostle's pond when Roche accosted her. He put a gun to her temple and forced her into the woods. 'All I can remember is the fear,' she told the court.
As Roche forced her to her knees and began to indecently molest her Mrs Hardy called out to Jesus. Roche yelled 'let Jesus save you now' and rained blows on her head with the butt of his air pistol.
He beat her so savagely that a friend who came across her a few minutes later only recognised her because of the two dogs she had with her.
An off-duty police officer, Helen Brown, who was also walking her dogs on the common, gave first aid, enabling Mrs Hardy to breathe until an ambulance arrived. She spent a month in hospital.
Roche, who worked occasionally in factories, had been sleeping rough in his car for four days before the attack after being thrown out of his parents' home.
Before his arrest he moved in with a girlfriend, who has since had his child. The court was told she intends to stand by him.
Jeremy Gompertz QC told the court in a plea in mitigation for Roche that doctors found no mental abnormalities when they examined him. Because of that, and as he had no similar previous convictions, Mr Gompertz said, 'it would be wrong to draw the conclusion this man is necessarily a danger to the public and women in particular'.
But Mr Justice Mitchell said Roche 'could only be regarded as thoroughly dangerous and therefore someone from the public must be protected'. He recommended that Roche should serve eight years of the life sentence before he was even considered for parole.
Mrs Hardy, who is still receiving treatment for injuries which left her permanently disfigured and with damaged sight and hearing, was not in court to see Roche sentenced.
A detective, who telephoned her after sentence was passed, told reporters: 'She is very pleased he has been put away for life - more for the general public than for herself. She feels very sorry for the family. She is just relieved it is all over and done with.'
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