Believing there is a possibility beyond the physical laws, or a potential or freedom that transcends appearances, is the same thing as believing a Higher Power and disbelieving that the ego's laws have complete power over what happens.
Even if you can't see God or Jesus, or you are not even sure if they really exist, if you have even a little willingness - which is all the Course asks us to have - this is an invitation to the Holy Spirit. It's not just a little willingness to be mistaken, but a willingness to be open to a source of healing and truth which is more true than how things currently appear.
This works both in the areas of healing your illusory mistaken perceptions, in which your willingness invites Holy Spirit to correct your mind, but also in the grander area of the entire illusion, in which your willingness invites Holy Spirit to perform demonstrations of miracles through you for others.
Your mind has the ability to open itself to connect to a Source of miracles even if the majority of the mind is still in the dark. If there is enough of a "leap of faith", this will create a pipeline across which the Power of God can flow. You are able to them become a conduit for the Holy Spirit to work through you, in spite of you having a large body of delusions of your own that need to as yet be corrected.
Reaching outside the illusory world to join with God is all that it takes. Some measure of belief in the real truth. Many people just don't as yet realize that it is as easy as this, and so don't act in the role of extender of God's love through miracle working. You may not realize that you really only need to have some faith/trust and believe in the truth in order to now be a vessel for Holy Spirit to flow through.
A vast majority of miracles performed in the world today are performed by students of whatever spiritual system, students who are still "in process" of awakening and who are still learning about the truth. They do not need to be completely purified in order for such miracles to work through them, if they have willingess to allow Holy Spirit to "use them" and work with them.
Some trust in God is all it takes, a little willingness to accept that God's truth is true.