N3
ことはない
There is no need to, Never happens
そんなに慌てることはない。まだ時間がいっぱいあるからゆっくりやればいいよ。
There is no need to rush that much. We still have a lot of time, so it is okay if you pace yourself.
Explanation
「ことはない」 has 2 uses
1No need to
Dictionary form + ことはない: there is no need to...; often said to reassure: 「そんなに心配することはないよ」. 何も～ことはない = there is nothing to...
そんなに急ぐことはない。ぼちぼちやればいい。
There is no need to hurry. You should take your time.
そんなに慌てることはない。まだ時間がいっぱいあるからゆっくりやればいいよ。
There is no need to rush that much. We still have a lot of time, so it is okay if you pace yourself.
2Never happens
Dictionary form + ことはない: something will not (or will never) happen, often with もう or だろう: 「もうあの家に帰ることはないだろう」.
１０年前に親と喧嘩をしてから、親と話すことはない。
Ever since I fought with my parents 10 years ago, I have not talked to them.
もうあの家に帰ることはないだろう。
I'll probably never go back to that house.
Mixed up with
It sounds like advice from above, so don't use it to a boss or elder. To equals and juniors it is a gentle reassurance.
Don't confuse it with past form + 「ことはない」: dictionary form means 'no need to'; past form means 'have never': 「富士山に登ったことはない」 (I've never climbed Mt. Fuji).
「なくてもいい」 gives permission ('you may skip it'); 「ことはない」 is a judgment ('no need at all'), usually soothing.