This means that they are not trusting in God, but rather in their idea of God. They are trusting in an idol, which has been created with their own mind. They might call it 'God' , but it is not the true God of the Bible. We must first hear God speak before we can begin to trust in what we think He has said. Of course this begins when the Holy Spirit convicts a person of their sin, and the person then turns to God exercising faith for salvation.
Grace is an undeserved favor or gift.
There is nothing that a person can do to deserve grace. No large number of good deeds will in any way 'qualify' a person so that they deserve grace. If they deserve it, then it is no longer grace. It is important that we understand 'when' we are truly exercising faith, and when we are not. Then we can live a life that includes decisions not to continue doing those things that are contrary to the life of true faith.