God, of course. Logically, or philosophically, there is no getting away from Him. (We traditionally understand "Him" as "Father" - it doesnt mean he is an old fella sitting on a cloud somewhere).
In the West today, religion is much diminished - because people have so many other distractions to lose themselves in, so much temporal pleasure to indulge in etc. And people are so deeply jaded in the modern day too, there is such great beauty, mystery and miracles all around us, every day, yet they do not see it, or dismiss it with a sneer like an overgrown teenager.
In the UK, after the failure of protestantism (CofE, CofS etc), people are happy spending their lives in front of the TV, or in the pub, or gym etc. Few people give any thought to how they will spend eternity.
It doesn't help that false religions only rush to affirm whatever secular society does or says, rather than challenge it in any way, or offer an alternative. People rightly see that as bogus and as offering them nothing they do not already have.
We have a fleeting existence in this world, we should be concerned about what will become of us in the next. We are born to know, love and serve God in this world - one of the chief ways in which we do this is to strive live according to His will (which is tough) - and be happy with Him forever, in the next.
Not to diss anyone's opinion, but oftentimes people dismiss God on the most frivolous of grounds. For example, people seem to think that because "bad things happen" then that means there could be no God. But, without bad or challenging things to overcome, what would this life be other than a meaningless puppet show?
One of the reasons bad things happen, if because God has given us free will - and some people abuse that gift to do wrong. And we should realise that there is great meaning in everything, even in suffering and hardship.
People also seem to think that they are capable of fully understanding God and that God must appear to be accountable and rational to their human mind. This is a great mistake - believe in God, or not, its not unreasonable to see that puny creatures such as ourselves could not fully comprehend Him.
And so, of course, there is much about life and God which we cannot fully grasp.
For my thoughts are not your thoughts: nor your ways my ways, saith the Lord.
I respect people being skeptical and asking questions etc, but I marvel at people who are happy just to bumble along through life and never give a second though about where they have come from, and where they are going.