We owe our access to vincent van gogh's thoughts and feelings about many of his paintings to:

I think the most straightforward answer tot his question are the letters van Gogh wrote/drew, but we can also access van gogh's thoughts and feeling through his works and paintings. His style evolved a lot during his life, and his works can consist of paintings and also sketches. his frequent use of certain colours can also represent his feelings. After his death, his mother disposed of many of his works, but most of them were left to his brother Theo. Letters exchanged between Vincent and Theo also give us a running commentary to van Gogh's life and thoughts at the time.