No, we do not believe those who have passed became angels. Angels are beings quite separate from mankind. The Bible is pretty clear on that:
When I consider thy heavens, the work of thy fingers, the moon and the stars, which thou hast ordained; What is man, that thou art mindful of him? and the son of man, that thou visitest him? For thou hast made him a little lower than the angels, and hast crowned him with glory and honour. (Psalms 8:3-5 KJV)
A little lower than the angels, David said. Paul said a bit more:
Know ye not that we shall judge angels? how much more things that pertain to this life? (1 Corinthians 6:3 KJV)
Before we get to the point of doing that bit of judging, though, there are things for us to accomplish here. We have ministries to serve, people to witness to, service to provide in the name of our Lord. Our hope and our work go way beyond things on earth. If we only hope for things here, our hope is in vain.
If in this life only we have hope in Christ, we are of all men most miserable. (1 Corinthians 15:19 KJV)
Our hope is not only in this life – but in Christ’s promise and His resurrection. 1 Corinthians 15 has much to say on this subject, and one of my favorites is:
For this corruptible must put on incorruption, and this mortal must put on immortality. (1 Corinthians 15:53 KJV)
I believe, as did Mary Frye:
Well, actually, my body will. There is no hesitation about saying that, and no doubt that it will happen. I’ve made certain arrangements, paid an attorney to write down what should be done when – not if – that occurs. For anyone to be in denial about the certainty of death borders on being psychotic. It is inevitable. Before then, I have a lot of things to do.
One of those things is to stand each Christmas with a group of people as we remember loved ones no longer standing beside us. The lights remind us of the light of the world, too:
Then spake Jesus again unto them, saying, I am the light of the world: he that followeth me shall not walk in darkness, but shall have the light of life. (John 8:12 KJV)