question #1 Sahih Muslim Introduction 32, Introduction, Narration 31 : Why is the chain of narration considered crucial in the authentication of hadiths?

‘The chain of narration is from the Dīn, and were it not for the chain of narration whoever wished could say what he wanted’.Muhammad bin Abd Allah said, al-Abbās bin Abī Rizmah narrated to me, he said I heard Abd Allah [bin al-Mubārak] saying: ‘Between us and the people are ‘the legs’ (meaning the chain of narration, i.e. if a Ḥadīth was like a creature)’.Muhammad said, I heard Abā Ishāq Ibrāhīm bin Īsā at-Tālqānī say, I said to Abd Allah bin al-Mubārak: ‘Oh Abā Abd ir-Rahman! How is the Ḥadīth which goes ‘Indeed from al-Birr after al-Birr is that you pray for your parents after you pray for yourself and you fast for them both after you fast for yourself’? So [Ibn al-Mubārak] said: ‘Oh Abā Ishāq! On whose authority is this?’ I said to him: ‘This is a Ḥadīth from Shihāb bin Khirāsh’. [Ibn al-Mubārak] said: ‘[He is] trustworthy. On whose authority [did he transmit]?’ I said: ‘on authority of al-Hajjāj bin Dīnār’. [Ibn al-Mubārak] said: ‘[He is] trustworthy. On whose authority [did he transmit]?’ I said: ‘He [al-Hajjāj said] the Messenger of Allah, peace and blessings of Allah upon him, said…’ [Ibn al-Mubārak] said: ‘Oh Abā Ishāq! Indeed between al-Hajjāj bin Dīnār and the Prophet, peace and blessings of Allah upon him, is a wilderness in which the necks of the mounts are severed, however, there is no difference of opinion regarding charity [offered on behalf of one’s parents]’.Muhammad said, I heard Alī bin Shaqīq saying, I heard Abd Allah bin al-Mubārak saying in front of the people: ‘Abandon the Ḥadīth of Amr bin Thābit for indeed he would curse the Salaf [i.e., the Companions, may Allah be pleased with them]’.