Essentially You must, strengthen and improve your certainty.
For when certainty prevails in the heart and establishes itself therein the unseen becomes as if seen,
as 'Imam Ali, may God honour his face, the cousin and son-in-law of prophet Muhammed
said: 'had the veils being removed, it would not increase my certainty.' in relation to existence of God and his angels including paradise and hell.
know that Certainty is power, firmness and stability of the faith so great that it becomes as a towering mountain which no doubts can shake and illusions disappear completely,
and when the doubts and illusions come from external/outside are
neither listened to by the ear nor heeded by the heart.
The Devil cannot approach the possessor of such certainty;
Actually the devil instantly flees from that person,
fears his very shadow, and is content to keep at a
safe distance. As the Messenger of God, may blessings and
peace be upon him, has said: 'Satan is afraid of the shadow of Omar,
and Omar never takes a road but that Satan takes
another. Certainty derives its power and excellence from many things.
The first, most essential and pivotal of these is that the person listen attentively
with his heart as well as his ears to verses of Quran and hadiths relating to God,
His Majesty, Perfection, Magnitude, and Grandeur, His Uniqueness in creating and deciding,
ruling and compelling; likewise to the truthfulness and perfection of the Messengers,
the miracles they were aided with, and punishment for those who disbelieve God
opposed them. That these are sufficient to bring about certainty is indicated by His Word in the Quran that
(Exalted is He!): Is it not enough for them (humanity) that We have sent down upon you the Book(Quran)
which is recited to them?

The second is to learn from looking at the kingdom of the heavens and the earth,
and the wondrous and astounding creatures that God made them teem with.
That this brings about certainty is indicated by His saying (Exalted is He!): We
shall show them Our signs on the horizons and within themselves
until it becomes clear to them that it is the Truth. .....
The second is to learn from looking at the kingdom of the
heavens and the earth, and the wondrous and astounding
creatures that God made them and guided them. That this brings
about certainty, is indicated by His saying (Exalted is He!): We
shall show them Our signs on the horizons and within themselves
until it becomes clear to them that it is the Truth.

The third is to behave according to what one believes,
outwardly and inwardly, zealously, and to the limits of one's
resources. That this brings about certainty is indicated by His
saying (Exalted is He!): Those who strive in Us, We shall surely
guide them to Our ways.

Proper certainty results in, among many other things, ac-
quiescence in God's promise, confidence in what He has
guaranteed, turning to God with pure longing, abandoning all
things which distract from Him, continuously returning to
Him in all circumstances, and spending all one's energy in
seeking His good pleasure.

In sum, certainty is the essential thing, and all other noble
ranks, praiseworthy traits of character and good works are its
branches and results.

Virtues and actions are strong or weak, sound or unsound,
according to the strength or otherwise of certainty. Luqman,
upon whom be peace, said: 'Action is possible only in the
presence of certainty; a servant acts in obedience only to the
extent that he has certainty, and a man becomes neglectful in
his actions only when his certainty diminishes.' This is why
the Messenger of God, may blessings and peace be upon him,
has said: 'Certainty is the whole of faith,'

Believers have three degrees of certainty. The first is that of
the People of the Right Hand, 10 this is firm belief but with the
possibility of becoming doubtful or shaky under certain circumstances.
This is called faith.The second is that of the Ones Brought Nigh, which is the
possession of the heart by faith and its establishing itself
therein so firmly that its opposite becomes no longer possible