Major Sins preventing one from entering Paradise
Allah (swt) has informed us of the major sins that will prevent us from entering Paradise, these are:
Committing shirk, associating partners with Allah
A highway robber
Harboring any amount of arrogance
Until one’s debt is forgiven or paid
A person whose neighbor is not safe from his mischief
One who has oppressed or wronged someone. He will need to make amends to the person in this life, or the person wronged will get his right on the Day of Judgment.
The early generation, at the Prophet’s time, also used to say that the believers will be held at the doors of paradise for 100 years for a sin they committed.
This hadith indicates if a person fulfills the minimum requirements and avoids the forbidden acts, he has earned paradise. However, we are still obligated to fulfill our responsibilities, act properly, and keep away from sins. Also, voluntary actions are encouraged to help us get closer to Allah, make up for any shortcomings, and to wipe out minor sins.
Sources:
[1], [2], and [3]: http://abdurrahman.org/sunnah/nawavi40explanation.html