Prince George Alexander Louis, the son of the Duke and Duchess of Cambridge William and Catherine, will be christened at 3pm today in the Royal Chapel at St James's Palace by Archbishop Justin Welby. The prince, who was born on 22 July at St Mary's Hospital in London, is third in line to the throne.

In a short video released by Lambeth Palace, the Archbishop of Canterbury described the event as "hugely important" and significant for anyone, whoever they are. Prince George will join two billion people around the world in "the family of the Church", he said.

Explaining what will happen when he christens Prince George, the Archbishop said: "I will mark Prince George with the sign of the cross on his forehead. It's an extraordinary moment because that is the sign by which we understand that this person belongs to God."

The Archbishop hopes the ceremony might encourage anyone who is thinking about christening or baptism – either for themselves or their child – to go along to their local church and find out more.

Steve Clifford, general director of the Evangelical Alliance, said: "We are delighted that all over the country people are today celebrating the birth of Prince George. As he and his family come together for this ceremony we are praying for them all.

"As we look to the future, we are all praying that he will have the opportunity, as an adult, to freely commit himself to the Christian faith."

In the video the Archbishop also said he hoped people would not view baptism as only for a future king or for special people. "God's love is offered without qualification, without price, without cost, to all people, in all circumstances, always," he said.

Rev Mike Talbot, chair of the Evangelical Alliance board, said: "The arrival of Prince George, as with any child, is a cause for great rejoicing. His parents undoubtedly want the best for him, and are evidently ready to do that not simply because of what family tradition might dictate.

"It is very encouraging to know that they clearly see the importance of the spiritual, as well as physical and emotional, aspects of development. Having him baptised is putting him on the first step of a spiritual stairway."

Following the christening, a picture will be released showing the Queen with three future monarchs – the Prince of Wales, Prince William and Prince George and the Royal Mint is to create a set of commemorative coins to mark the occasion.