Everything that is from God is perfect, 100%, absolute. So if God gives me faith, I'm sure about him, there is no doubt. There is nothing any more that can take this knowledge of God from me. I just know in my heart, that now God exists in my life, he is here.
Faith can be imagined like a telephone line between God and man. God has established a connection between him and me. Now I can get easily in contact with him at any time. It is now in my hand how many times I get in contact with God and how the relationship to him is arranged. He is definitely here, for sure.
But what are the conditions that God establishes this connection to me? God, that means your creator wants you, he wants you to give your life to him. Not more and not less. He wants you lock, stock and barrel, completely. He wants your life, your thoughts, your worries, your family, your possessions, he wants all of you, all that you are and not are. God does not do things by halves. Only the one who gives him everything gets everything. If you surrender your life to God, he will establish the connection between him and you and you will know God. You'll be able to see him and know who he is and also who you are. There will be no questions and no doubts.