Hi gnoll. It seems to me that your pastor is using the word 'believe' in two different ways. Our belief in God is, among other things, the trusting faith that He exists. God doesn't 'believe' in us in that sense of the word - He created us, so there is no need for Him to have that kind of faith. Perhaps your pastor meant that God believes in us in the way that we might say to another person "I believe in you", meaning that we are encouraging them, telling them that we love them, etc. In that sense, yes, God 'believes in us', although I wouldn't have put it quite that way. :)
2 Thess 2:16-17 Now may our Lord Jesus Christ himself, and God our Father, who loved us and gave us eternal comfort and good hope through grace, comfort your hearts and establish them in every good work and word.