A more thorough explanation:

A Keeper of the Great Seal is an important officer in England and Scotland who is responsible for keeping and using the Great Seal to authenticate important state documents. This officer is also known as the Lord Keeper of the Great Seal, Lord Keeper, Keeper of the Broad Seal, or Custos Sigilli.

In England, the Lord Chancellor is currently responsible for the duties of the Keeper of the Great Seal. This means that the Lord Chancellor is the one who has custody of the Great Seal and uses it to authenticate important state documents.

For example, if the Queen of England wants to issue a royal proclamation, the Lord Chancellor would use the Great Seal to authenticate the document. This would make the proclamation an official state document that carries the weight of the government behind it.

Another example would be if the Prime Minister of Scotland wanted to issue a decree, the Keeper of the Great Seal of Scotland would use the Great Seal to authenticate the document. This would make the decree an official state document that carries the weight of the Scottish government behind it.