Q. How do we understand the purpose of our life?

 If you seek truly, you are bound to get it. God will certainly take us to the next step forward. Like Cardinal Newman says 

Lead kindly light, Lead thou me on,
Amidst the encircling gloom,
Lead Thou me on,
Yet one step enough for me.

All we need is that one step, because the distance we need to travel may unnerve us. Each step is to be positively inclined. So if you think good, see good, talk good, do good, only good will result. And Good and God are synonymous.

The first line (of the reply) may also be interpreted thus: if you seek the Truth, you are bound to attain it. And Truth and God are synonymous.