¶ Let all the house of Israel therefore know for certain that God has made him both Lord and Christ, this Jesus whom you crucified.”
It seems that in order to have faith in God we have to "know" certain things. Some people have a highly unrealistic idea of faith when it comes to faith in God. This is because they define faith as the absence of doubts. For these people, faith is not valid unless it is certain. Thus, when the inevitable doubts come that challenge their faith in God and His Word, they feel that they never really had the kind of "faith" necessary to be a true believer. But this is not the Bible's picture of faith...
How many things do you know for "certain"? Compare this with how many things you know. If you're like most people, according to Prof J.P. Moreland, you probably think about 500 things a day that you accept as true yet without absolute certainty.
Faith is only faith in the presence of doubts. While Scripture commends that we know certain things it only once asks us to know something for certain - that Jesus is Lord (Acts 2:36). We can know, trust and love God yet battle with doubts. Of this, I'm certain.