What is the test for changing the meaning of a word in a deed?

In Smith v. Packhurst (1741), 26 E.R. 881, Lord Chief Justice Willies stated: "Another maxim is, that such a construction should be made of the words in a deed, as is most agreeable to the intention of the grantor, the words are not the principal things in a deed, but the intent and design of the grantor; we have no power indeed to alter the words or to insert words which are not in the deed, but we may and ought to construe the words in a manner the most agreeable to the meaning of the grantor, and may reject any words that are merely insensible ..."