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I assure you I will make the most of every opportunity I have at your company.

I promise you ...

You have my words that I ...

Do all of the above convey the same idea to you? Thanks.
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Ant_222My view:

A promise is when you assume an obligation to do something for that person.

This is OK.

For
assuring: I want to make you feel relaxed/confident by telling you something
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When you assure someone of something, you tell them that they can be sure of it. It's a pledge of your sincerity.
When you promise or give your word1, you take an obligation upon yourself; you commit yourself to some future action.

They are really very different. One does not "keep an assurance" or "fulfill an assurance" as one "keeps a promise" or "fulfills a promise" or "keeps one's word". (But it's not idiomatic to say "fulfill one's word".)

(1You have my words that ...)

CJ
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Comments  
My view:

A promise is when you assume an obligation to do something for that person.

Assuring someone is more like taking a responsibility for your words.
 Marius Hancu's reply was promoted to an answer.
 CalifJim's reply was promoted to an answer.
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CalifJimWhen you assure someone of something, you tell them that they can be sure of it. It's a pledge of your sincerity.
When you promise or give your word1, you take an obligation upon yourself; you commit yourself to some future action.

They are really very different. One does not "keep an assurance" or "fulfill an assurance" as one "keeps a promise" or "fulfills a promise" or "keeps one's word". (But it's not idiomatic to say "fulfill one's word".)

(1You have my words that ...)

CJ

Thanks, Ant, Marius, and Jim.

Got it.