1. To a lot of people, God is just a bigger version of themselves, or the product of their idealism, or an amalgam of different things brought in so they can feel better about universalism and stuff. I find this to be an incorrect belief: a kind of idolatry. But I suppose I can see how secularists would try to generally attribute this to all believers, since some do it. I maintain, however, that God IS WHO HE IS, regardless of who we want Him to be. In other words, He is a real and actual entity.
2. Interestingly, the question in the quote is more upside down than the writer knew. Christians are supposed to have a huge interest in this world: in living each day fully according to God's will and working hard for Him until it's time to go home. A lot of people think they can just get baptized and then continue along doing whatever they used to do and wait for death. That was never really the plan. But since some do it, I can see how secularists would generalize it.
3. Thinking little of oneself is generally a good attribute. With that preoccupation out of the way, it gives them time to think of others. "A life spent to the fullest" should not be confused with a life spent in hedonism. And I don't necessarily mean wild debauchery when I say "hedonism". I simply mean the single-minded servitude of self, whatever that looks like for the individual. But why should one not do that if one will entirely cease to exist in a few decades or less? Or perhaps you will cite acts of service or opportunities of self-deprivation like dieting and exercise as a counterpoint. But why do people do these things? In a secular view, are not acts of service done to make others think more highly of you, to feel better about oneself, and/or to receive some kind of compensation in the form of a tax break, favorable PR, etc.? Do not diet and exercise have the aim of making oneself more attractive, thus gaining a higher degree of adoration (theoretically) from others?