Substance is first given form in the mind, and as it becomes manifest it goes through a threefold activity. In laying hold of substance in the mind and bringing it into manifestation, we play a most important part. We do it according to our decree. "Thou shalt decree a thing, and it shall be established unto thee."
We are always decreeing, sometimes consciously, often unconsciously, and with every thought and word we are increasing or diminishing the threefold activity of substance. The resulting manifestation conforms to our thought, "As he thinketh within himself, so is he."
There is no scarcity of the air you breathe. There is plenty of air, all you will ever need, but if you close your lungs and refuse to breathe, you will not get it and may suffocate for lack of air. When you recognize the presence of abundance of air and open your lungs to breathe it deeply, you get a larger inspiration.
This is exactly what you should do with your mind in regard to substance. There is an all-sufficiency of all things, just as there is an all-sufficiency of air. The only lack is our own lack of appropriation. We must seek the kingdom of God and appropriate it aright before things will be added to us in fullness.