What can a person do to enter Paradise and avoid waiting 50,000 years on the plains of gathering, and what is God's wisdom in this waiting?

Entering Paradise is a great aspiration, made easy for those whom Allah wills it to be easy for. The gathering (on the Day of Judgment) is inevitable for all creation, but the gathering of the believer will be gentle and easy. As for wisdom, Allah Almighty possesses ultimate wisdom in all His actions. This wisdom may be apparent to us or it may be hidden. What is hidden from us, we entrust to Allah's knowledge, and we believe in His ultimate wisdom.