Why can I know I am forgiven?
You can know you are forgiven because forgiveness is part of God's all-inclusive work of salvation, accomplished instantly the moment you believe. It is not confirmed by feelings or personal perfection, but by taking God at His word—because the book says so, and that is faith.
Les explains that salvation is the all-inclusive work of God on our behalf. What does He do? He forgives us, justifies us, sanctifies us, glorifies us, baptizes us into the body, seals us with the Holy Spirit, fills us with the Holy Spirit, and more—all accomplished instantly the moment we believe. Les stresses you will not necessarily feel these things; you won't feel glorified, see a halo, sprout wings, or see the sky green instead of blue. But how do you know these things happened? The book says so. That's where faith comes in: taking God at His word. So you can say, yes, I know I'm forgiven, not because you're so perfect or better than anybody, but simply because you can believe what this book says.