I have spent my whole life telling people that I cannot explain why tragedy overtakes some and not others.

I have also spent my whole life despairing of those who offer inane platitudes and trite responses to those whose lives are torn apart by tragedy or disaster. This week I am perplexed once again. I have nothing to say that adequately expresses my sorrow and sadness for the people of Nepal and my heart aches when I hear the Nepalese Transport Minister Tek Bahadur Garung say: "This catastrophe has overwhelmed Nepal's government, we don't know what to do in such a situation ... this is very hard ... it's a mess."

Even those who still have houses are camped outdoors. The tectonic plates have dealt them the severest of blows, but fear of what might happen in the aftershocks extends the agony for people who have already lost everything.

I hear that the death toll is 5,000 and rising and I hear that up to eight million people may have been affected by this disaster. They were already amongst the poorest people in the world. Where does this leave them? I hear some people asking where is God in all of this? If it's God's world can't God make a better job of running it? Well, if you want a sterile discussion about God then start with questions like that; however, if you want a real encounter with God then start with the way that women and men, in their common humanity, respond to the needs of those who are overtaken by the extremes of nature. So, short of falling into the platitudes trap I am driven to some kind of action because, as Edward Guest first said: "I'd rather see a sermon than hear one any day."

I can stay shocked for a long time and I can be angry that, because Nepal is a poor country, Kathmandu isn't built like San Francisco; but what good does that do? Instead, I need to work with others to meet the immediate needs of those who are suffering and I need to work for the kind of change across the world that will allow the people of Kathmandu, and others like them, to live in safe houses and share the same hopes and expectations of life as I enjoy. And I believe that if I do that then I am engaging with God at a level that is way beyond the sterile and banal.

This Saturday, with many others, I will be climbing Ben Lomond. This was to be a sponsored outing to raise awareness of and raise funds for the work of Christian Aid, but what was a good intention has become an urgent cause. Christian Aid is one of the many charities that have launched special appeals in response to the earthquake in Nepal, so, as of today, the decision has been taken that every penny raised on Ben Lomond will go directly to the Nepal Earthquake Appeal.

I have a mountain to climb and it will be sore on my old knees; but Ben Lomond is as nothing compared to the mountain that has to be climbed by the people of Nepal and my discomfort will be as nothing compared to the suffering of the Nepalese people. They cannot recover from this catastrophe without help from every possible source around the world, so get sponsored and come with me on Saturday as we walk and pray for the people of Nepal. Sign up at: http://act.christianaid.org.uk/ea-action/action?ea.client.id=48&ea.campaign.id=31523 or if you can't you can't climb with us please sponsor me at: https://70munros.everydayhero.com/uk/rt-rev-john-chalmers

Christian Aid's Regional Emergency Manager for South Asia has said: "We have dispatched 74,000 water purification sachets, which will provide at least 744,000 litres of safe drinking water for those affected and we will also be providing 5,000 tarpaulins to meet the need for emergency shelter." This just a start and you may say it is but a drop in a bucket; however, "a dripping tap soon fills a bucket" and every donation gratefully received will find its way into this giant bucket of human need.

The Rt Rev John Chalmers is Moderator of the General Assembly of the Church of Scotland.