It might be proper legal doctrine and not just puffery to impress the natives:

“The words, on which the plaintiff relies, as creating a covenant, are these: “To have and to hold, &c. she said Horatio yielding and paying to James Borland, his heirs, &c. yearly and every year, so long as grass shall grow, or water run, the full and just sum of 25 dollars.” These word constitute an express covenant, and not a mere covenant by implication of law.
[Reports of Cases Argued and Determined in the Supreme Court of the State of Vermont, Vol. IX, 1838]