What is the effect of supplication on the believer's soul, along with examples?

Du’a has a profound effect on the soul; it brings tranquility to the heart and expansion to the chest. It is an act of worship, and through it comes success and guidance, the removal of worry, grief, and distress, and the arrival of relief and joy. It also repels affliction. Frequent supplication makes the supplicant feel the sweetness of closeness to Allah.