If you know that reality was created by a God; and that the creator God is a person who loves you as a person (because God is your spiritual parent) - then this is a good reason for believing that your life has purpose and meaning.
Why? Because God has both created your world and you - and because that God is loving (like an ideal parent), thus you can assume that there is some purpose for your life specifically, and some meaning to the details of your life.
A civilization in which many or most people believe that the world and their own life has meaning and purpose, will have reason be motivated to live, and to live in certain ways that accord with the assumed intentions of God.
One who believes in a loving parent creator will regard reality as not just purposive and meaningful - but overall benign. He will believe that the good things of life are deliberate, and the bad things of life are either not intended or in some way necessary (if when this is not understood).
Conversely - if a person decides that 'God is Dead' - that there is No-God and never was; then reality is not created but instead regarded as random, unintended, and indifferent to him personally.
He regards his life as ultimately accidental - he is adrift.
Stuff happens but means nothing. Anything that seems good is not really good. Truth, Beauty, Virtue may seem to be things in the world - but are Not really real.
Any apparent purpose or meaning, any-thing that appears hope-full; are actually a deceptive superficial appearance. They will be taken-for-granted. There is no reason to feel grateful for your life - because there is no intent to do you good.
By contrast; all adversity and suffering are to-be-expected (because, why not?).
Indeed - the adversity and suffering of life are taken as evidence that there is No-God.
In essence: When it is assumed there is No-God; all that is good and pleasant is explained-away as the delusive surface appearance of random or determined indifferent processes - while all that is bad and unpleasant are taken as evidence that there is No-God...
After a while, in a world where God is excluded as a reality from all serious public discourse, God is forgotten.
The assumptions are inverted; and people forget the inversion has happened (has, in fact, been chosen) - and forget that it is an assumption.
The assumption of No-God becomes reinterpreted as an inference from what seems like evidence...
The inference of the atheist is that I am (of course!) alienated in a world with neither purpose nor meaning; and the reality of life is quite naturally adversity and suffering, because there is No-God.
When things are bad - why not? What do you expect as an insignificant speck in an infinite world? But when things seem good, you are just fooling yourself.
Evidence wherever he looks! (Any counter-evidence is just wishful thinking.)
For the atheist; there is no reason to do anything in particular unless there is a rapid, sure and significant pay-off in terms of feeling better. He lives in a world only of micro-motivations - because no other motivations can be really real, all must be manipulations or illusions.
Whereas the original inference was that because there Is God (creator and loving parent) - therefore, the deep reality of my life is always and everywhere one of ultimate meaning and purpose.
The contrast between God and No-God is between the reality of purpose, meaning and a benign world - and the problem is to know this; and the reality of existing adrift in an arbitrary existence where only short-term personal pleasure or pain are solidly-real.