Let's let O'Sensei speak for himself.
From "The Aikido FAQ" Web site at www.aikidofaq.com
An interview with Morihei Ueshiba O Sensei and Kisshomaru Ueshiba
The interview, conducted by two unnamed newspapermen, appeared in the Japanese-language text "Aikido" by Kisshomaru Ueshiba, Tokyo, Kowado, 1957, pages 198-219. It was translated from Japanese by Stanley Pranin and Katsuaki Terasawa.
Q: It is said that Aikido is quite different from Karate and Judo.
O Sensei: In my opinion, it can be said to be the true martial art. The reason for this is that it is a martial art based on universal truth. This universe is composed of many different parts, and yet the universe as a whole is united as a family and symbolizes the ultimate state of peace. Holding such a view of the universe, Aikido cannot be anything but a martial art of love. It cannot be a martial art of violence. For this reason Aikido can be said to be another manifestation of the Creator of the universe. In other words, Aikido is like a giant (immense in nature).
Therefore, in Aikido, heaven and earth become the training grounds. The state of mind of the Aikidoist must be peaceful and totally nonviolent. That is to say, that special state of mind which brings violence into a state of harmony.
And this I think is the true spirit of Japanese martial arts. We have been given this earth to transform into a heaven on earth. Warlike activity is totally out of place.