In the incident when Musa upon him be peace instructed the Bani Israel to sacrifice a cow that Allah had demanded of them for the purpose of giving thanks to show gratitude for emancipation from bondage of the evil of Pharaoh. The children of Israel thought that Musa upon him be peace was mocking them yet Musa upon him be peace was telling them that he seeks refuge in Allah from those who act foolishly and ignorantly without knowledge.
So the Bani Israel were reluctant to sacrifice a cow through unnecessary questions made the difficulty of the simple task for themselves and Allah made it more difficult for them because of their attitude. They started to question Musa upon him be peace different criteria as to what type of cow it should be when there are a wide variety of cows in colour and breed. So they were going back and forth with questions about the type of cow until it was determined by Allah that it would be a bright white yellowish cow neither too old or too young, neither used to till the soil nor water its fields, it must be wholesome without any blemish. To find such a cow cost them time, effort and more money and all aspects made them even more reluctant even after deliberation, to slaughter and sacrifice the cow, had they at the initial command of sacrificing a cow, then any cow would have been sufficient but due to unnecessary questions, reluctance and obstinacy they made it difficult and their heart was not in the desired sacrifice meaning they did not want to obey and make the matter easier for themselves so Allah made life more difficult for them in this situation.
The Tawrah states that the cow as reddish without blemish with all the other criteria however this is an error and the correct opinion is that the cow was a deep yellowish white that was pleasing to look at. The lesson from this incident is that a person when they understand that Allah SWT has legislated and commanded them simply hearing and obeying is sufficient for placing you heart with sincerity in the task to ensure Allah SWT is pleased and that Allah is sufficient and accepts the efforts made by those who hear and obey without unnecessary questions and simple make the task as simple to facilitate the acceptance by Allah what is prescribed by Allah SWT.
Also making life difficult for yourself through reluctance and obstinacy particularly with making the one who was sent to guide them and teach them, this difficulty they bring upon themselves through the aspects of questioning something that is already easy to understand and follow yet there is no gratitude and being ungrateful males life more difficult and the blessing is taken away by Allah and a person only realises when that blessing is gone and then needs to reflect as to why they made life difficult for themselves and others causing them to lose heart and find misery and anguish as a result of not hearing, obeying, understanding, following the messenger upon them be peace and the commands of Allah SWT.