From the Lectures on Faith 3:2-5:
Let us here observe, that three things are necessary, in order that any rational and intelligent being may exercise faith in God, unto life and salvation:I have quoted this passage many times on my blog. It is center to my faith and walk with God.
First, the idea that he actually exists.
Second, a correct idea of his character, perfections and attributes.
Third, an actual knowledge that the course of life which he is pursuing, is according to his will.