In the UK we would say 'at Easter.' If you are talking about the specific day we would say 'on Easter Sunday/Monday' etc. So I guess it depends which variant of English you are interested in. Saying 'on Easter' would be considered incorrect here.

You need to use "at Easter". It's a festival, ie. a point in the cycle of a year. You only use "on" if you mean a particular day, eg. "on Easter Sunday". I've done a quick check using news articles (UK, US, etc), and it's very uncommon to use "on Easter" by itself, if you mean the festival as a time. I'd also consider using "on" in this context as incorrect.

“On Easter,” is used in the U.S. “One tradition in my family is eating lamb on Easter.” “Also, in the United States, children receive candy and presents on Easter.”

When do we use the infinitive to with ing? for ex, the Key to forgiving Is....why don t we say the Key to forgive Is... ?...Is there a rule?