Corporate identity is the group of design elements which transmit a same and only business message, and that make up the company's image. The importance of the group, as regards its construction, is its homogeneity. It is very important that the group is consistent and that its elements transmit the same message. This does not mean you need to have a lot of uniform elements, but that every element must exploit its features in order to transmit the same message and respect the same visual consistency which immediately identifies it with the company it represents.
The logo is the essential element in this issue: it is the fundamental and foundational element of the corporate identity. It is the fundamental element since, without a logo, a company cannot even operate. The logo is not only the representative image of the company: the company cannot sell a thing without it. Let's see it through an example.
You want to buy a DVD player for your home. You go around the shop and see different models, brands and prices until you find one you like and which is at a good price. You examine it and decide to buy it; but, suddenly, you notice that you have not seen its logo yet; i.e., you do not know who manufactured it. Then, you look for the logo; you do it carefully but you do not find it. What do you do? Would you spend money on a device which you do not know who manufactures it, where it comes from, nor who is responsible for it? Of course not; nobody would. That is the reason why the logo is fundamental for a company to operate.
The logo is the foundational element of the corporate identity since, as we have seen, it is necessarily the first and most important one; therefore, it is from it that all parameters are created. Designers base on the logo to create any other design and that is how it must be done. The logo is the founder of the criteria which all the other elements of the corporate identity group must meet.