WHEN YOU ARE WITH SOMEBODY you love, you have little if any sense of the passage of time, and you also have, in the fullest sense of the phrase, a good time.
When you are with God, you have something like the same experience. The biblical term for the experience is eternal life. Another is heaven.
What does it mean to be "with God"? It doesn't mean you have to be thinking about being with God, or feeling religious, or sitting in church, or saying your prayers, though it might mean any or all of these. It doesn't even mean you have to believe in God.
To say that a person is "with it" is slang for saying that whether he's playing an electric guitar or just watching the clouds roll by, he's so caught up in what he's doing and so totally himself while he's doing it that there's none of him left over to be doing anything else with in the back of his head or out of the corner of his eye. It's slang for saying that the temperature where she is is about forty degrees hotter than the temperature where she is not, and that whatever it is everybody's looking for, she's found it, and that if she were a flag and they ran her up the mast, we'd all have to salute whether we liked it or not. And the chances are we'd like it.
Being "with it " may not be the same as being with God, but it comes close.
We think of eternal life, if we think of it at all, as what happens when life ends. We would do better to think of it as what happens when life begins.
Saint Paul uses the phrase eternal life to describe the end and goal of the process of salvation. Elsewhere he writes the same thing in a remarkable sentence in which he says that the whole purpose of God's slogging around through the muck of history and of our own individual histories is somehow to prod us, jolly us, worry us, cajole us, and, if need be, bludgeon us into reaching "maturity . . . the measure of the full stature of Christ" (Ephesians 4:13).
In other words, to live eternal life in the full and final sense is to be with God as Christ is with him, and with each other as Christ is with us.