How can someone integrate the Buddhist philosophy on life's purpose into daily life? The question 'What is the purpose of life?' has been asked before. What I understood is that if I were to set a purpose to life, once I achieve my goal, life becomes meaning less. There is no single thought great enough to spend an entire lifetime. So, life has no intrinsic meaning.
In everyday life, we try to plan things. Setting goals provide clarity about what exactly to do, what's important and what's not. Reaching goals help building self-confidence and motivates to move forward. It also helps to work efficiently while dealing with big tasks (Makes big tasks into smaller, more manageable units, Helps good decision making that are inline with the final goal).
Both sound reasonable to me but they also seem contradictory. Then how should a lay man approach his life to be productive and at the same time seek liberation from the sufferings of samsara?
The essence of dukkha (suffering) is clash, conflict, discord, disharmony - of some kind, whether inner conflict in one person's mind or outer conflict between persons or groups of people.
The opposite of that is happiness, whose essence is peace and harmony.
A lay person could make meaningful contribution to society and make progress towards liberation from samsara by dedicating his or her life to reducing the causes of suffering and creating causes of happiness.
Specifically, reducing, preventing, reconciling inner and outer conflicts and helping with implementation of behaviors that lead to peace and harmony.
For example, a professional peacemaker/negotiator in armed conflicts is someone who resolves external conflicts. Resolving external conflicts he or she removes causes of suffering. Making peace he or she creates causes of happiness.
You can come up with more ideas like this. A psychologist reduces suffering that happens due to inner conflicts. A teacher reduces suffering that happens due to ignorance and confusion.
Various professions work in different areas and have different level of influence: some work at individual level and some work with large groups of people.
The important thing to realize is what I started my answer with. As long as your job is reducing causes of suffering such as conflicts, clashes, greed, hatred, confusion, ignorance - you will both make a nice contribution to society and make progress on the Path.