Belief and certainty are two different scopes in faith yet the two are used simultaneously as though antonym yet as synonym.
Belief has ambiguity made in to certainty by putting variant phenomena of unseen faith in to unseen confidence thereby making probability as possibility and belief as conviction
On the other hand, certainty has display of conviction that proves ones belief explaining truth confidence and passionate belief as certainty.
Belief is confidence on conviction and certainty is conviction in love.
Belief is living life in conviction and certainty is giving life in conviction.
In my opinion, belief is a verbal accord in life and certainty is expressional element of displaying fact as life after death.
Belief is spending life in probability and certainty is sacrificing life for vanity therefore certainty.
And here is the explanation of the Aya of Quran “ Kehdoe Tum Islaam laa-aey ho Eman Nahee”
There is always a difference between an ambiguous belief and a certain belief.
The parameter of belief and certain belief though are similar yet seeing is the truth that creates difference.
You see it you say it and when you are certain you do it.
This is like one praising for life and the other praying for death as martyr.
The difference between Shia and Sunni Muslims has the effect off same reflection.
Sunni believes and Shia’s are certain. (Dr Raza)