Allah (swt) saved the Arc of the Prophet Nuh (PBUH) to make it a sign, a reminder and a warner. Allah (swt) says:

 إِنَّ هَٰذِهِ تَذْكِرَةٌ ۖ فَمَن شَاءَ اتَّخَذَ إِلَىٰ رَبِّهِ سَبِيلًا 

(Indeed, this is a reminder, so he who wills may take to his Lord a way.) (Al-Insan: 29)

(… تَذْكِرَةً… ) (…a reminder…): Meaning, the story of the annihilation of the people of Nuh (PBUH) is a reminder for the people. We should always remember this story to avoid doing the same. Not just a reminder but also:

(  وَتَعِيَهَا أُذُنٌ وَاعِيَةٌ… ) (…and [that] a conscious ear would be conscious of it): A conscious ear remembers what it hears and keeps a lesson of it. In this regard, Qatada ibn an-Nu’man (may Allah be pleased of him) said: “A conscious ear is an ear which listens, understand and comprehend”. The one who has a conscious ear does not commit the sins of the previous people to avoid being punished as such.

Allah (swt) describes the ear as being conscious though consciousness is a characteristic of the heart, whereas for the ear has the hearing sense. This is because when the ear listens carefully it conveys what it hears to the heart which becomes fully aware and act accordingly. Conscious means to keep something in your mind or your heart and act according to it. Hence, the conscious ear benefits from what it hears.