Ṣadr (plural ṣudūr) is the chest or breast, that part of one which faces what confronts one. It is where the battles and dramas take place. It must be remembered that every drama is self-created. Every imaginable human role stirs in the breast of man: the king, the despot, the afflicted, the jealous, the strong, the doubter, and the complainer. We have to take refuge from these, take refuge in the Lord Whose mercy brings us to the recognition that everything which occurs, visible and invisible, occurs according to a just system, according to perfect laws which govern this passage, this journey through the creation.
By Shaykh Fadhlalla Haeri from the book “Beams of Illumination from the Divine Revelation – A Commentary on the Last Section of the Qur’an”