‘Abdullāh ibn ‘Amr ibn al-‘Ās reported: The Messenger of Allah (may Allah’s peace and blessings be upon him) said: "Verily, Imān (faith) wears out within one of you as a shirt becomes worn out; so ask Allah to renew Imān in your hearts." Sahih/Authentic. - [Al-Haakim]
Imān (faith) wears out and weakens in a Muslim's heart due to slackness in worship or commission of sins and involvement in pleasures. Indeed, faith wears out as new clothing wears out due to long use. So, the Prophet (may Allah’s peace and blessings be upon him) told us to ask Allah Almighty to renew and increase our faith, through supplication, good deeds, performance of the obligatory and voluntary acts of worship, and frequent dhikr and pursuit of Allah's forgiveness. The Hadīth also indicates that giving parables was part of the Prophet's approach in educating.