Allah is Most Merciful and the source of all goodness, so, why does He not admit us all to Paradise without reckoning?

As a matter of fact, Allah wants all His slaves to have faith.

{And He does not approve of disbelief for His slaves. If you are grateful, He approves that for you. No bearer of burden can bear the burden of another. Then to your Lord is your return, and He will inform you of what you used to do. He is All-Knowing of what is in the hearts.} [312] Surat az-Zumar: 7.

However, if Allah sends all people to Paradise without reckoning, this will be a flagrant violation of justice. It means that Allah will treat His Prophet Moses and the Pharaoh the same way and will admit every oppressor along with his victims to Paradise as if nothing happened at all. There is a need for a mechanism that ensures that those admitted to Paradise will be admitted based on eligibility.

The beauty of the Islamic teachings lies in the fact that Allah, Who knows us better than we know ourselves, informs us that we possess the necessary qualifications to utilize the worldly means and attain His pleasure and enter Paradise.

{Allah does not burden any soul greater than it can bear...} [313] Surat al-Baqarah: 286.