Whenever you do a walkthrough, just do the following.
1. State that you applied at McKinsey for 2-4 reasons (nice signposting)
2. List the 2-4 highlights from your resume that led you towards your application with the firm (top-down communication)
3. Discuss briefly each of these and how it encouraged you on your journey to work in consulting and for McKinsey (storytelling)
The highlights should focus on more recent and the most relevant experiences and tell a story of how your resume led you to consulting.
An example (from an actual candidate of mine):
1. Even though I studied a non-business degree at <uni 1>, I got interested in management issues during <experience 1> and <experience 2>
2. First, after my studies I started to work in the healthcare industry, took over the project lead of <project 1>, and made first arrays into leadership and problem-solving.... Second, ...
3. Throughout my resume I have had many diverse experiences and this is something that I want to continue as a consultant. <Achievement / learning 1> guided me further to ...