Fatalaqqa adamu min rabbihi kalimatin fataba AAalayhi innahu huwa attawwabu arraheem (surah Baqarah: 37)

Tafseer Tafheem-ul-Quran by Syed Abu-al-A'la Maududi

(2:37) At that time Adam learnt appropriate words from his Lord and repented, *51 and his Lord accepted his repentance, for He is very Relenting and very Merciful. *52

Fatalaqqaaa Aadamu mir Rabbihee Kalimaatin fataaba `alayh; innahoo Huwat Tawwaabur Raheem

*51). This means that when Adam became conscious of his act of sin and wanted to return from his state of disobedience to that of obedience, and when he tried to seek remission for his sin from God, he was unable to find the words to use in his prayer to God. In His Mercy God taught him the words with which he could pray.
The word tawbah basically denotes 'to come back, to turn towards someone'. Tawbah, on the part of man, signifies that he has given up his attitude of disobedience and has returned to submission and obedience to God. The same word used in respect of God means that He has mercifully turned towards His repentant servant so that the latter has once more become an object of His compassionate attention.
*52). The Qur'an refutes the doctrine that certain consequences necessarily follow from sins and that man must in all cases bear them. In fact this is one of the most misleading doctrines to have been invented by human imagination. If it were true it would mean that a sinner would never have the opportunity to have his repentance accepted. It is a mechanistic view of reward and punishment and thus prevents and discourages the sinner from trying to improve.
The Qur'an, on the contrary, tells man that reward for good actions and punishment for bad ones rests entirely with God. The reward that one receives for good acts is not the natural consequence of those acts; it is rather due to the grace and benevolence of God and it is entirely up to Him to reward one or not. Likewise, punishment for evil deeds is not a natural and unalterable consequence of man's acts. God has full authority to punish man for his sin as well as to pardon him.
God's grace and mercy, however, are interrelated with His wisdom. Since He is wise, He does not use His power arbitrarily. Hence, whenever God rewards a man for his good acts, He does so because the good was done with purity of intention and for the sake of pleasing God. And if God refuses to accept an act of apparent goodness, He does so because that act had merely the form or appearance of goodness, and was not motivated by the desire to please God.
In the same way God punishes man for those sins which he commits with rebellious bolness, and which whet his appetite for more rather than lead him to repentance. Similarly, in His mercy God pardons those sins which are followed by genuine repentance and readiness on the part of the sinner to reform himself. There is no need for the criminal to despair of God's grace and mercy, no matter how great a criminal he is. Nor is there any reason for even the most rabid disbeliever to despair, provided he recognizes his error, repents of his disobedience and is ready to replace his former disobedience with obedience.