I was reading the thread and also interested that so few people mentioned faith.
My faith is hugely important to me and my underlying values system. I also work and have young children. Both of these are important to my sense of purpose. My job is vocational, and I view it as part of a career which involves social justice, using my personal power and privilege for the benefit of society and vulnerable individuals. I would like my faith to play a bigger role in my daily minute by minute sense of purpose but I have struggled to maintain that focus since family life has become demanding. I also used to make more of a community contribution, through voluntary, faith related stuff. But I have had to drop that as other demands have increased. I feel quite pared back from all my previous interests, and can totally see how, once family life is less demanding, I will have to re orient and re focus myself.
There are loads of exercises you can do to help find your purpose (life coaching type stuff), but I think being in touch with your core values and sense of what has always been a natural drive for you as a person really helps.
Also, I love a project (goal and then sense of achievement when conplete), and I love a list, so have lists of life goals, medium term goals and short term goals. I even have lists of frivolous goals, eg visiting lavender fields etc (though I find it hard to prioritise this over eg what the kids might enjoy). I find these make a huge difference in terms of achievement of those goals, and my overall sense of a directed purposeful life. Obviously one has to be flexible too, to allow for life. There were some threads on here about different sorts of lists which helped me with this, though I can't remember what they were called.