I regard it as a simple fact that the thinking of a single person can change the world, and for the better.
1. It is "thinking" that has the effect, not necessarily a physical-action.
2. As little as one person thinking may be effectual, not necessarily any group, institution or nation.
3. "Change the world", i.e. the 'external' world: the world (including people) outside the 'brain' of the thinker.
4. "For the better", which is change-positively and in line with the will and intention of God.
(Provoking widespread negative change is easy and common - a spiteful gossip can do it; but I am here talking about a positive and personal contribution to all of divine creation.)
It may be helpful to draw together the assumptions that lie behind such a statement.
1. Thoughts are actions in the real world.
(I was originally convinced of this by Rudolf Steiner's Truth and Knowledge, and The Philosophy of Freedom; and the work of Owen Barfield - such as Saving the Appearances.)
2. We live in A Creation - and God is the creator, loves us and is concerned with us each as individuals -- all human beings constitute (in some literal sense) God's family of children.
3. Therefore, God is able and willing - through His ongoing-creation - to take-up, amplify and spread-through-creation any specific thought (or other action) from any one of His Children - when this thought contributes positively to the goals of creation.
Our main business, therefore; is to think good, positive thoughts - true, beautiful, virtuous; and if we do this, then God can and will take-up these thoughts; and make of them what He will in the world at large.