Pope Francis wept in response to a question sent to him by a person in care asking why his mother had abandoned him as a child, the Vatican has revealed.

The pope cried when he read the question ahead of a meeting last month with minors living in foster care or receiving other forms of support from the Romanian-based NGO, FDP, or Protagonists in Education.

The Vatican has released a written transcript of the encounter, including details of the pope's response to the question that prompted his tears.

That question, which the young man read aloud to the pope, was why his mother did not want or accept him. He explained that he was given up when he was 2 months old and when he turned 21 he got in touch with his birth mother and even stayed with her for two weeks. But the encounter did not go well and he was forced to leave.

'My father is dead. Am I at fault if she doesn't want me? Why doesn't she accept me?' the unidentified man asked the pope, who received a list of questions before the meeting.

The pope responded: 'I want to be sincere with you. When I read your question, before giving the instructions for my speech, I wept. I was close to you with a few tears...Your mother loves you, but she doesn't know how to, she doesn't know how to express it. She can't because life is hard and unjust, and that love that is trapped inside her, she doesn't know how to say it or how to caress you.'

He urged the young man to hold on to hope and not despair or become cynical. 'I promise to pray that one day she can show you that love,' the pope said.

Another person asked: 'Why are there parents who love healthy children, but not those who are sick or who have problems?'

Francis explained that in this difficult world, some people are too weak to express their love, partly because of their social conditions including poverty.

'If I have a giant rock, I can't put it on top of a cardboard box because the rock will crush the box,' he said, adding that some adults 'don't have sufficient strength to bear fragility because they themselves are fragile'.

The pope went on: 'It's a question of the immense fragility in adults, due to, in your case, much poverty, many social injustices that crush the smallest and the poorest.'

He added that 'spiritual poverty' can also be to blame, because it leads to 'hardened hearts, and it causes what seems impossible: a mother who abandons her own child. This is fruit of material and spiritual poverty, fruit of a mistaken, inhuman social system that hardens hearts, that leads to mistakes, makes it so we cannot find the right path.'

Pope Francis stressed that parents have their own vulnerabilities, 'And perhaps they were not lucky to be helped when they were young'.

The pope continued: 'It's difficult to get help from fragile parents and sometimes it's us who has to help them' and use one's own strength so 'the rock doesn't crush the cardboard box'.

Another young person said that when a friend at the orphanage had died, an Orthodox priest had told them the boy died a sinner and would not go to heaven. Pope Francis said no one can ever claim that anyone – even Judas – has not gone to heaven. 'God wants to bring all of us to heaven, nobody excluded,' he said.

God, Pope Francis said, is the Good Shepherd who is always searching for the lost sheep and is never upset when he finds them, even if they are 'dirty with sin' or have been abandoned for their whole lives.

'He embraces them and kisses them,' puts them on his shoulders and brings them home, the Pope said, adding 'I am sure this is what ... the Lord did with your friend.'