The first key is knowledge.
We must know what the blood has done. No one can apply it if he is ignorant about it. We must study it, learn it, know it. What did the blood do, and what will it now do?
The second key is faith in what we know.
Let faith arise in our hearts. How can we apply the blood unless we believe what we are saying?
The third key is declaration by faith of what we know.
To declare means to speak out loud. If I know it and believe it, then I will speak it—not as though by magic or superstitiously, but by faith in God, who never lies.