An interesting question. One hears this blessing in many countries and from many people. Even strangers who hear you sneeze will say it. There is so much one could say about blessings but I will limit myself to the issue of sneezing and a few comments on the faith aspect of blessing.
It appears that the practice of blessing sneezers originated in ancient Greek or Roman times or even earlier but no one really knows. In 77 AD, Pliny the Elder, a Roman naturalist, asked the same question wondering why Tiberius Caesar, who was most unsociable, would insist on a salutation when one sneezes.
According to the librarian at the Folklore Institute at Indiana University, this custom comes from the idea that you are sneezing out your soul. People thought the soul was flighty and could separate from the body, escaping through the sneeze or through a yawn, leaving one open to evil spirits. A variation of this idea is that the heart stops when you sneeze.
Some believe that because sneezing indicated the onset of illness, a blessing was invoked for protection in a world with no antibiotics. That seems to me to be the most logical reason for the practice. No one really knows for sure. But it does seem to be a lovely custom.
What does it mean to bless? The dictionary defines blessing as invoking divine care for, conferring prosperity or happiness; praising and glorifying; speaking gratefully of.
We see many examples of God's blessings in the Old Testament. God appears to Jacob in a dream and tells him that he will be blessed with land, descendants and protection. However, God's blessings do not simply consist of power, fertility and prosperity but show the positive relationship between the bestower and the receiver of the blessing.
God's blessing is bestowed on the patriarchs and the prophets. The Psalms repeatedly bless God as do many other parts of the Old Testament. As a matter of fact, the whole Old Testament is the story of God's blessings on the chosen people.
God's blessings abound in the New Testament also. Jesus blesses and reaches out to all: to the suffering, to sinners, to the most abandoned, even to those who confront and challenge him. Many times the word "bless" is used. Remember the Beatitudes and who is blessed in them.
Blessings in the Church's ritual are too numerous to count. There is blessing throughout the Eucharistic Liturgy with phrases such as "The Lord be with you," as well as at the end with the formal blessing.
Blessings are a part of every sacrament from the beginnings of life in Baptism to its ending in the Anointing and the funeral liturgy. We use holy water, blessed candles, blessed palms. Children are blessed by parents. Throats are blessed on the feast of St. Blaise.
God blesses, thought the blessing is not deserved. God accepts humans with their limitations. As a matter of fact, God seems to prefer those who are the weakest as shown in many Scripture stories.
It seems as if God is saying not, "Are you strong and holy enough to do my work," but instead, "Are you weak and trusting enough that I will work through you and accomplish great things?"
After all, Jesus said we should become like little children to enter the kingdom of heaven.
Blessings are a part of our everyday life. We give them and receive them daily - a smile, a kind word, a sign of forgiveness. Blessing begets blessing. When we bless others, we too are blessed and love grows in us.
As we call God's blessings upon one another both through word and deed, we can truly say with the book of Numbers 6:24-26: "May God's face shine upon you and be gracious to you. May God lift up his countenance on you and give you peace."
May we, in God's name, shine our faces upon one another and be gracious to one another and thus bring blessings of peace and joy to one another from day to day.
I've often wondered why we say "God bless" or "bless you" when a person sneezes.