To think is to have a particular opinion, belief, or idea about someone or something.
To know is to a : to be aware of the truth or factuality of : be convinced or certain of b : to have a practical understanding of <knows how to write>
My nine years old daughter refuses to say think when talking about God. She corrects me each time I say think in regards to a promise that we have from God. She tells me there is a huge difference between think and know. I never really thought about it. She said to say I think is to be somewhat in doubt but to know is to fully trust God at His word.
Do you think or do you know?