When someone asks the purpose of life, the answer can become a bit convoluted - but the simple and universal answer is to be happy.
On this, I think, everyone agrees - everyone seeks a happy life.
The differences come when considering the scope of 'life'.
The three main variables are:
1. Time-scale - short-term versus long-term
There are trade-offs between being happy immediately and being as happy as possible overall, across life; between the immediate certainty of here-and-now happiness by doing exactly what you want, and deferring happiness now - or accepting suffering - as an investment in building less-certain but potentially greater happiness later.
2. Mortal life versus post-mortal life
The modern secular person is concerned only by happiness during mortal life, but most religious people are concerned with happiness across a life which extends beyond mortality. Therefore the scope of a happy life varies in duration between a finite (but uncertain) number of hours, days or decades; up to some greater unit than mortality, which varies between religions and extends up to infinity.
3. Personal happiness versus the happiness of a larger unit
There is a wide variation in the understanding of that unit whose happiness is to be pursued and maximized. At one extreme it is just me - the individual; but beyond that there are many increasingly larger units of all believers; the family, tribe, nation; all humans, the living world - potentially up to the whole existing universe.
If it is assumed that the desire for a happiness is intrinsic and universal, this scheme can be used to classify all religions (whether private or public) in terms of whether the aimed-at happiness is now or later, for mortal life or beyond, and just for me or some larger group.
Both the modern secular hedonist and the devout Christian seek a happy,
but the differences in attitudes and behaviour may be vast - not because
they conceptualize happiness differently, but because they perceive
reality differently; and therefore conceptualize the scope of happiness and the scope of life differently.
If you see 'life' as ending in death, and only concerning your-self, then a strategy of maximizing happiness leads to quite different results from a person who sees 'life' as extending beyond death and encompassing others people - past, present and/or future.
All people are the same insofar as they all want to be happy, their aim is to have a happy life; and differences between people can be reduced to differences in the perceived nature of reality.
[Note: Differences between people 'can be' reduced to differences in perceived nature of reality - and this is enlightening in some ways; but this analysis (this kind of analysis) is necessarily a reduction. Meaning that much is left-out by it. To put it mildly.]