Quran

Allah commands fearing Him when paying back the debt as well as when acknowledging its receipt, in order to honor the rights of people and warn against what causes corruption. Al-Alusi: 3/63.
Question: Allah commands fearing Him upon fulfillment and again upon acknowledgment. Why?

The heart is described as (sinful) because concealment is a deed of the heart. The heart is a lump of flesh that when it is sound, the whole body becomes sound. Al-Qurtubi: 4/478.
Question: Why is heart described as (sinful)?

These good rulings to which Allah has guided his servants, include great wisdom and serve great purposes, indicating that if people followed Allah's guidance, their worldly and spiritual affairs would be sound, as these rulings include justice and that which is in their best interests; their rights would be protected, quarrels and conflicts would be prevented, and people's livelihood would be satisfactory. Al-Saadi: 119-120.
Question: What makes people affairs, both worldly and spiritual, sound?

Giving priority to hearing and obedience over asking for forgiveness is giving priority to the means over the request, and that makes the supplication more likely to be accepted and answered by Allah. Al-Alusi: 3/69.
Question: Hearing and obeying are mentioned before requesting forgiveness. Why?

In principle, the commands and prohibitions are not too difficult for people to adhere to; rather, they are nourishment for the soul, remedy for the body, and protection from harm. Allah commanded the servants what He commanded them out of mercy and kindness. Al-Saadi: 120.
Question: Sharia's laws and teachings are mercy and kindness from Allah. Explain in light of this verse.

(For it), this expression is used for good deeds because a person rejoices in earning them and are added to his possession. (Against it), this is used for bad deeds because they are like burdens and sins and hard to bear. This is like saying: "I have wealth" and "I owe a debt." Al-Qurtubi: 4/500.
Question: Explain the use of these words: (for it) and (against it).

(Pardon us), for whatever between us and You of what You know of our shortcomings and misdeeds. (And grant us forgiveness), for whatever between us and Your servants, thus, do not expose our sins and evil deeds to them. (And have mercy upon us), do not let us fall into another sin. It is said that a sinner needs three things: Allah's forgiveness for what is between him and Allah, that Allah conceals his sins from His servants, thus He does not disgrace him among them, and that Allah protects him so that he does not fall into the same. Ibn Kathir: 1/324.
Question: A sinner needs three things. What are they?