In 2001, Keshubhai Patel's health was failing and the BJP lost a few state assembly seats in by-elections. Allegations of abuse of power, corruption and poor administration were made, and Patel's standing had been damaged by his administration's handling of the earthquake in Bhuj in 2001. The BJP national leadership sought a new candidate for the chief ministership, and Modi, who had expressed misgivings about Patel's administration, was chosen as a replacement. Although Advani did not want to ostracise Patel and was concerned about Modi's lack of experience in government, Modi declined an offer to be Patel's deputy chief minister, telling Advani and Atal Bihari Vajpayee that he was "going to be fully responsible for Gujarat or not at all". On 3 October 2001 he replaced Patel as chief minister of Gujarat, with the responsibility of preparing the BJP for the December 2002 elections. On 7 October, he was sworn in, and entered the Gujarat state legislature on 24 February 2002 by winning a by-election to the Rajkot – II constituency, defeating Ashwin Mehta of the INC.
Why was Advani concerned about Modi’s appointment as a chief minister of Gujarat?
For Modi being a candidate  for the chief minister of Gujarat, Advani was concerned about Modi’s lack of political experience.