Fear is a sin, and indeed one of the very worst of sins - a sin that is capable of singlehandedly wrecking the whole of a human life.
I don't mean fear as an emotion - that is just a matter of an evolutionary adaptation to threats... I mean existential fear: that is, fear as a mind-set, fear as a basic stance towards life.
For Christians, to live in a mind-set of fear is to deny the basics - to deny that God the creator is our loving Father. Fear is, indeed, a variant of despair - which is the assumption that God has placed us in a hope-less situation - which would mean that God did not love us or was not the creator of this world.
Fear is so basic, so pervasive, that it is a primary motivator for many people much of the time - whole religions, whole civilisations are built primarily on fear: fear of the gods or God, fear of Life, fear of reality...
Christians have often - and still do - deliberately create fear - and I mean existential fear, the worst kind, the worst kind of sin - as a way of supposedly enforcing faith. This is crazy if it is sincere... certainly it is wicked and counter-productive. When this happens, something has gone terribly wrong - sin has overcome the Christian message, the Gospel has been perverted.
Our lives can become absolutely dominated by fear; and this can even feel like a moral imperative. Morality gets mixed up with fear of hubris, superstitious fear that if we do NOT fear, then the fates will be revenged upon us...
Life, by this account, ought to be a continual submission, a continual propitiation, a continual attempt not to offend the tyrannical and jealous and vengeful forces that are assumed to control things... If we do NOT fear then we will be crushed, to teach us not to presume, teach us not be pride-full... The idea arises that continual and expected and mandatory fear is the core way of avoiding pride. Fear becomes a duty.
The fear-full are prone to inculcate this same existential dread in others - perhaps on the excuse that people need to be afraid or else they will not avoid sin... But this is an appalling thing to do to others - fear can rapidly and permanently get out of control, grow like a cancer in a person or a community - and kill it. Eternally kill it.
Systematically to inculcate existential fear is a double sin - because, unlike personal sins, it is deliberate and avoidable - and this requires repentance even more than fear in oneself.
Existential fear is NOT Christian, it is a failure of faith...
If we do fear then it must be repented; and I mean must - not because we will be punished by God if we don't repent our fear, but that by fearing we have already rejected God implicitly... we have already rejected the God of love and rejected our relationship with him... We have specifically rejected the fact that he is our loving Father and we are instead insisting that God is a tyrant who requires that we live in continual and systematic terror.
So fear is a sin, and a terrible sin which can destroy everything: it must be repented. We need to want to be free of fear, we need to aspire to a sublime confidence about life: that is what God wants from us.