When a man says the same thing again and again, it is a sign that he speaks the truth, or, at least, that he would be thought so to do; yes, if an honest man do clearly, fully, plainly, often engage himself to us in the same thing, we count it a vile jealousy not to believe the real truth of his intentions. Now, the Lord in his promises often speaks the same things,—he speaks once and twice. There is not any thing that he has promised us but he has done it again and again. For instance, as if he should say, “I will be merciful to your sins;” I pray believe me, for “I will pardon your iniquities;” yea, it shall be so,— “I will blot out your transgressions as a cloud.”
There is not any want whereunto we are liable, but thus he has dealt concerning it. As his command is line upon line, so is his promise. And this is one way whereby God causes the truth of his promises to appear. To take away all color of staggering, he speaks once, yea twice, if we will hear.
from a sermon entitled The Steadfastness of the Promises, and Sinfulness of Staggering; volume 8 of Works, page 222