Being a Christian does not make you a better or happier person.
That is not what Jesus Christ promises, and not what he aims primarily to 'deliver'.
That is not what Christianity is properly "about".
Christianity - at core - is (or ought to be!) about salvation; and salvation is saving an individual from "death", and instead enabling him (by following Jesus Christ) to become resurrected to eternal life, in Heaven.
Yet there is a relationship between "not of this world" Christianity, and the conduct and experience of this mortal life on earth.
And this can be seen by the contrast with that ideology of materialism-atheism-leftism, that dominates (all-but monopolizes) public discourse; especially (although not exclusively) at the highest levels of power; and especially in The West.
This belief system - which has, in practice, infiltrated the leadership and laity of almost all self-identified religions, and has now coopted all the major Western churches (including Christian churches) in their core affiliations - we will here term the materialist-atheist ideology.
Christian belief does not make you a better person. But it does mean that you want to attain salvation; want, that is, to follow Jesus Christ to resurrected everlasting life in Heaven.
And to enter Heaven requires that you desire to live eternally in complete harmony with God's will, with the motivations of divine creation.
To attain salvation does not require that you actually attain harmony with the divine, while alive mortally on earth - or else Heaven would be empty!
But you need to want to do it!
Such a desire may positively affect your conduct in this mortal life. So there is an indirect relationship between Christianity, and being a better person.
To be a materialist atheist does not of itself make you an evil-aligned person.
But it does mean that you have no reason - except momentary expediency - to be a better person.
And it does mean that you have no coherent basis for understanding what a 'better person' might be.
What about a happier life for Christians?
Well, that is not promised; and the basic nature of this world is unchanged by becoming a Christian. All Christians are subject to the 'entropic', corruptive, degenerative nature of this world - and all will die.
(Indeed all Christians need to die; if they are to attain their heart's desire.)
Yet, insofar as existential 'alienation', meaninglessness, and purposelessness - a sense of the futility of all relationships and actions - are all major dissatisfactions of modern life; then the Christian understanding does provide a positive and hopeful framework - such that miseries with these roots can be known as temporary and not ultimate.
Whereas, for a materialist-atheist, there is no ultimate or permanent reason to be happy.
Happiness is understood to be merely an evanescent response to psychological, bodily, and environmental events. So, to be happy doesn't mean anything and doesn't last.
On the plus side; the materialist atheist has no ultimate restrictions (such as would apply to a Christian) on what he does in search of happiness. But, whatever extreme measures he might take; any consequent happiness can, in practice, only be momentary and meaningless.
And when the atheist-materialist is not currently happy; then there is no better context in which to experience this misery.
For the atheist-materialist; here-and-now misery can therefore be known as ultimate and overwhelming; despair can be absolute.
In sum; being a Christian certainly does not make you better or happier.
But following Jesus does provide an ultimate understanding of reality that can inspire and sustain betterness or happiness.
In particular; Christian conviction and affiliation is able both to explain why this mortal life is not the most important outcome in a life that extends to eternity; yet at the same time our lifetime choices may be of permanent significance - taken-up through resurrection into everlasting creation.
