You allow yourself to rest, to heal, to calm. And after a few minutes of practice you might switch into doing the third line-I am solid, I am free. This is not auto-suggestion. Because if you have succeeded in arriving in the here and in the now you are much freer. You are free from the past, from the future, from your worries, from your fear.
Solidity becomes a reality after a few minutes of arriving, of being home.
Solidity and freedom are two characteristics of nirvana. Nirvana is not something abstract. The Buddha said we can touch nirvana with our own body. So while you practice walking meditation you can begin to touch nirvana already with your body and your spirit. When you feel you are a little bit more solid, a little bit more free, then you begin to touch nirvana with your body and spirit.