The short answer to that question is because I was talking about Jesus’ birth, which happened a long time ago. When speaking about an event in the past, I use the past tense. What I wasn’t trying to convey was that either Jesus’ humanity or deity only existed in the past or for a limited time.
Of course, if Jesus is fully God, by definition, he cannot cease to be God. There aren’t too many Christians who have much trouble believing he was the divine second person of the trinity before the incarnation, continued to be so when he entered our world and still carried on as such when he ascended back to Heaven. Most Christians are fine with his being God.
Some, however, are a bit more hazy on his humanity. The person who raised the point was being fair enough. I remember speaking about how Jesus has forever limited the expression of his divine attributes by taking on a human nature that he still has now. He remains the man, Christ Jesus. One lady came up to me afterwards and said she had never heard that before. I asked her what she thought happened to Jesus’ human body and nature after his ascension. She didn’t really know, she just kind of assumed he went back to being God like he was before the incarnation. I gently explained that he never stopped being God, and remains fully God, but his taking upon himself a human nature which necessarily limited the expression of his divine attributes meant he has forever limited himself that way for our sake. Jesus doesn’t just pick up and throw off his humanity as it suits him. He now eternally exists as the God-man.
Interestingly, and I can’t remember when and where I heard this, but I recall Stuart Olyott recounting a fairly similar story. He began teaching that Jesus is now in Heaven in a real human body. He, apparently, was approached by somebody after his sermon who said they had never heard this before either. And there does seem to be a fairly significant number of people who, though they affirm Jesus’ real humanity in the incarnation, seem to think his humanity kind of stopped after his ascension. He’s now in Heaven, they think, unencumbered by his human nature functioning just as he did before his incarnation.
But the Bible says it isn’t so. There is one mediator between God and man, the man Christ Jesus. Jesus lived bodily, died bodily, rose again bodily, ascended bodily and is now in Heaven awaiting his bodily return. Jesus is still as much a man today – a real, fully human man – as he was 2000 years or so ago. His divine attributes – though all still there and never diminished in power – are forever limited in their expression (not their power) by his real human body. He submitted not only to entering our world, nor just the shame and pain of crucifixion, but to eternally limiting the expression of his divine attributes in his human body for our sake.
I think this is some of what Philippians 2 is getting at. Some of us think that Jesus offered a temporary sacrifice. Not temporary in the sense of having temporary consequences, or needing to be repeated, but in the sense that he sacrificed for a short while – 30 years and a nasty crucifixion – but then, after that, everything was hunky dory back to normal. But Jesus taking upon himself real human flesh had eternal consequences, not just for our salvation, but for him personally. He didn’t cease to be a man, but forever remains in a real human body. And with it, he has forever submitted to all the limitations and realities of being in a man. He has forever given up the full expression of his divine attributes, though he still retains them in his deity, because he submitted to entering our world, becoming one of us and bearing the eternal consequences ever after of all that entails.