How can we be sure that God exists and that we can know him personally?  Paul Little explains:

“Herbert Spencer, one of the populizers of agnosticism of a century ago, observed accurately that a bird has never been known to fly to out of space.  Therefore, he concluded by analogy that it is impossible for the finite to penetrate the infinite.  Even if God does exist we can never know him personally or anything about his existence.

Spencer was right when he observed birds never fly out into space.  His observation was correct, but his conclusion missed an important alternative possibility: God, the infinite Creator, could penetrate our finiteness – the infinite could penetrate the finite, thereby communicating to us what he is really like.

It is impossible for us to know conclusively whether God exists and what he is like unless he takes the initiative and reveals himself.  This, of course, is what God did.

His fullest revelation has been his invasion into human history in the person of Jesus Christ – we can understand him because he has lived among us.”

Paul Little, Know Why You Believe, 34, 37.