People, whether they believe in God or not, put their own meaning into their lives. If Christians did not have Christianity, they would then have to put a new meaning into their lives, but every single one of them has chosen Christianity to represent meaning: The tenants of Christianity are what put meaning into the lives of Christians, the tenants of Humanism are what put meaning into the lives of Humanists, Egoism is what puts meaning into the lives of Egoists etc… But these are all just ideas that dominate and control a person and lead that person into thinking that their lives even have meaning. Without a predefined meaning, the individual makes their own meaning and fulfils their life according to that meaning no matter what it is. The assumption that no predefined meaning renders a person’s life meaningless only displays arrogance on behalf of the person who chooses to make such a presumptuous clause.
And arrogance lacks wisdom.