A grant application is a marketing tool that presents a compelling justification for your request for funding and inspires a sponsor to invest in your project. A complete application may include many elements, but the core component, the project narrative, typically presents in a clear, cohesive and well-written manner:

What your idea is;
Where your idea fits in the current state of knowledge/respective field (context);
How your idea will be accomplished (e.g., what methods, techniques, approaches will be used, and the feasibility of your plans);
Why your “how” is the best strategy to take (i.e. rationale for each approach, method, technique, etc);
What challenges might be encountered and how you would overcome them;
What success looks like; and
So what? What is the significance of your idea -- how accomplishing it will advance your field, or otherwise contribute to society.

In addition, either the narrative or other components of the application should clearly convey that:

The applicant team is qualified and all necessary expertise is available to ensure successful completion of the proposed project
All necessary resources required to perform the project are available (i.e. space, equipment, access to special collections, infrastructure, etc.);
The financial resources requested are appropriate for the size of the project and approaches used and the total financial support from all sources is adequate.