In The Name of Allaah, The Most Merciful, The Bestower of Mercy
Allaah [The Most High] said: [ لَن يَنَالَ اللَّهَ لُحُومُهَا وَلَا دِمَاؤُهَا وَلَٰكِن يَنَالُهُ التَّقْوَىٰ مِنكُمْ ۚ كَذَٰلِكَ سَخَّرَهَا لَكُمْ لِتُكَبِّرُوا اللَّهَ عَلَىٰ مَا هَدَاكُمْ ۗ وَبَشِّرِ الْمُحْسِنِينَ – It is neither their meat nor their blood [i.e. the animals we sacrifice] that reaches Allah, but it is piety from you that reaches Him. Thus have We made them subject to you that you may magnify Allah for His Guidance to you. And give glad tidings (O Muhammad) to the Muhsinun (doers of good)]. [Surah Al-Hajj. Ayah 37]
[لَن يَنَالَ اللَّهَ لُحُومُهَا وَلَا دِمَاؤُهَا – It is neither their meat nor their blood] – meaning: The aim [or goal] behind them [i.e. the animals slaughtered as sacrifice] is not just to merely slaughter them, for neither does their meat nor blood reach Allaah because Allaah is [الْغَنِيُّ الْحَمِيدُ -The Independent One Who is Free of all Needs and The One Who is Deservedly Praised]; rather what reaches Allaah is the sincerity [in your hearts in relation to the performance of the deed]; hope for Allaah’s reward and having a righteous intention; [وَلَٰكِن يَنَالُهُ التَّقْوَىٰ مِنكُمْ ۚ – But it is piety from you that reaches Him].
So with regards to this, there is an urge towards sincerity in [the act] of sacrifice and that one’s intention is to seek the Face of Allaah [alone], and not out of boasting, show off and to be heard; nor merely following a custom. Likewise, this is [the goal behind] all acts of worship, for if they are not connected to sincerity and piety, then they are similar to skins that have no flesh and a body that has no soul.
[Source: An Excerpt from Tayseer Al-Kareem Ar-Rahmaan Fee Tafseer Kalaam Al-Mannaan’ by Imaam Sadi (rahimahullaah). Slightly paraphrased. Publisher Daar Ibn Hazm 1st ed. 1424 (Year 2003)]