Because without our sufferings we can't relate to the world. God is preparing us to be able to preach to all a bit at a time.
Through the understanding of other peoples problems because we have truly been there, we are able to stand beside them and say "i understand what you are going through". God brings us through the trials and sufferings.
If you have been a single parent you can relate to another single parent.
If you have been through divorce you can relate to another divorcee
If you have an illness you can relate to others with that illness.
Whether or not the trials of life have been resolved you can relate to others.
You can be a bridge in the gap where they can only see no hope. No future. You because of having faith in Jesus know that there is a future, there is hope.