Allah tells us about His servant, Messenger and close Friend, the leader of the monotheists and the father of all subsequent Prophets, from whom Quraysh were descended and claimed to have taken their religion. He disowned his father's and his people's worship of idols and said:
("Verily, I am innocent of what you worship, except Him Who created me; and verily, He will guide me." And he made it a Word lasting among his offspring,) The Word means the worship of Allah Alone with no partner or associate, and the denunciation of all gods apart from Him, i.e., La ilaha illallah. He left this word as an example to be followed by those of his progeny who were guided by Allah.
وَإِذْ قَالَ إِبْرَاهِيمُ (And [ recall ] when Ibrahim said to his father and to his people, 43:26) At the end of the previous verses, Allah Ta’ ala had stated that the 'mushrikin' (polytheists) of Arabia had no argument in favour of their 'shirk' (polytheism) except that they were carrying on the customs of their forefathers. Obviously, sticking to such customs against logical and historical arguments is far from truth and justice. Now the point made in the present verses is that, even if they are adamant on following their ancestors, why do they not follow Sayyidna Ibrahim (علیہ السلام) who is the most noble of their ancestors, and it is taken by themselves as a matter of pride to be among his offspring. He was not only a believer in 'tauhid' (Oneness of Allah) who emphatically directed all his children to remain adherent to this belief, but his life-long behavior also indicates that following forefathers against logical and historical proofs is not permissible. When he was ordained prophethood in the world, all his people were polytheists in pursuit of the customs of their forefathers, but he, instead of blindly following his forefathers, announced his dissociation from his people, according to the dictates of positive proofs; hence his declaration: إِنَّنِي بَرَاءٌ مِّمَّا تَعْبُدُونَ "I disown that which you worship" (43:26).
A man may do whatever he wants in this world, because he has ample opportunities to do so. For this reason, people harbour the misunderstanding that whatever they do must be right. They argue that, had they been wrong, they would not have achieved success by adopting the course that they did. Arguments of this kind are generally advanced by those who belong to the well-to-do class. But this is a serious misunderstanding. In this world, indulgence in any kind of behaviour may make headway because of the freedom given to human beings during their period of trial. But in the world of the Hereafter, the testing period will be over and, therefore, this opportunity will no longer exist for anybody there. In every age, the religion of the prophets was opposed and most of all by ancestral religion. Ancestors assume the status of the ‘great’ ones in the estimation of nations. As compared to them, the prophet of their own days appears lowly in stature. It therefore becomes impossible for them to renounce the religion of their great men in favour of that of a lesser mortal. But it is on account of their denial of these ‘small’ men that these nations have had to face horrendous punishments.
Uthmani text of the Madinah mushaf (King Fahd Complex). Translation: Saheeh International. Tafsir via Quran.com.
