Just before Shabbat this past Friday afternoon, I completed a 10-mile run, my longest training distance so far as I prepare for this year's London Marathon. Over the past 13 years, I have been fortunate to run London five times, raising an estimated total of £50,000 for various Jewish and non-Jewish charities over that period.
This year, I am running for Aish UK, the national Jewish educational organisation for which I am the COO, and have set myself the target of raising as much this time around as I did on my previous efforts combined (plus smash my previous personal best time!).
So you can imagine how disheartened I was to discover that organisers of the 2016 Marathon are potentially planning to hold the marathon during the festival of Pesach.
It is well known that the London Marathon raises more money for charitable causes than almost any other single event in the world. So it is very upsetting to think that I - and many other Jewish runners - will be unable to participate.
As a committed Jew, to me this is the equivalent of asking a committed Christian to run the marathon on Good Friday.
The impact of this timing conflict is significant. Hundreds of Jewish runners enter the London Marathon annually; well over 20 charities across the spectrum of the Jewish community were represented in the 2014 London Marathon alone and, most significantly, over £80,000 was raised by runners representing Jewish charities last year.
This figure does not include Jewish runners who ran for other charitable causes not directly linked to the Jewish community. It would be a real shame for Jews to be frozen out of taking part - not only because of the fundraising implications for Jewish charities but also because of the tremendous cultural significance of this great British institution.
In contrast, the New York Marathon - the only marathon in the world to rival London in terms of scale, pageantry and significance - always takes place on the first Sunday in November (in spite of the often terrible weather on the East Coast of the USA at that time of the year), for the simple reason that it can never clash with the Jewish festivals that traditionally occur during October.
As a society we have come so far in religious and cultural acceptance. It is entirely possible to be an observant Jew engaged in modern society - I worked previously in a bank in the City of London for six years without ever having to violate my commitment to Jewish law or observing Shabbat and the Jewish festivals.
Yet it is important, perhaps now more than ever, when religious fundamentalism and extremism threatens the fabric of our entire society that we respond to these conflicts when they arise.
As one unified voice, the Jewish community can help to bring about change.
There are two other available dates to run the 2016 Marathon and I hope that the organisers choose one of these options.
If not, there is much to be lost. Not just for the runners affected, for the charities they toil and earn precious funds for, and of course, for the many individuals supported by these good causes. But also for the diminishment of an iconic event replete with a wonderful tradition of being open and inclusive to all and committed to serving so many.
One of the great attractions of the London Marathon has always lay in the incredibly eclectic array of over 35 000 participants - fast and slow; famous and unknown; those in regular running gear and those dressed as enormous chocolate bars, rhinoceroses, fairies and superheroes.
People of every background, religion and ethnic origin imaginable compete side by side.
As a religious Jew who proudly represents his community and works for an organisation dedicated to building Jewish futures while also contributing to our broader society, it has been my privilege to be a part of this uplifting experience over the years.
I do hope that by changing the dates, the organisers of the London Marathon will allow that to continue.
Brian Rubenstein is COO of Aish UK/the Jewish Futures Trust