Christians will often point out to atheists that if there is no God, then there is no objective meaning and purpose to life. Atheists will typically respond by saying that they create their own meaning in life. They find meaning in what they do, in family, etc. There are at least four problems with this, however.
First, they are substituting subjective, proximate meaning for objective, transcendent meaning. When people ask what the meaning and purpose of life is, they are not asking for advice concerning what meaning and purpose they should invent for their life. They are searching for something transcendent. They are looking to discover something that is already there, not invent something new. By substituting objective, transcendent meaning for subjective, proximate meaning, the atheist is referring to an entirely different understanding of meaning.