Lavan and Besuel literally unable to object

בפסוק מה' יצא הדבר לא נוכל כו'.

On the verse, "From Hashem the matter has come forth; we cannot [speak to you bad or good]," etc.

Lavan and Besuel respond to Eliezer that the match of Rivkah and Yitzchak has clearly come from Hashem, so they cannot say anything for or against it.

אמת אמרו לא נוכל.

They spoke truthfully when they said, "we cannot."

Their words "we cannot" were literally true — not merely a polite concession, but a real inability.

כי אם שרצו לעכב לא יכלו לפתוח פיהם ולעכב ומזה ידעו כי מה' הוא.

For even if they had wanted to hold it up, they were unable to open their mouths and delay it — and from this they knew that it was from Hashem.

Even had they wished to obstruct the shidduch, they found themselves physically unable to voice any objection. This very inability is how they recognized that the matter came from Hashem.

כי הלא רשעים היו והמה רוצין לעבור פי ה' ומה אמרו מה' יצא הדבר ע"כ לא נוכל.

For behold, they were wicked, and they wished to transgress the word of Hashem — so why did they say, "From Hashem the matter has come forth, therefore we cannot"?

The Sefas Emes raises the difficulty: Lavan and Besuel were resha'im who would gladly defy Hashem's will, so why would they suddenly submit, saying "we cannot" oppose what comes from Hashem?

רק הפי' כנ"ל שלא יכלו באמת לדבר מטוב ועד רע כנ"ל:

Rather, the explanation is as above — that they truly could not speak anything from good to bad, as above.

The resolution is that their submission was not voluntary piety. Hashem literally robbed them of the power of speech, so that they genuinely could not utter a word "from good to bad" — and that compelled silence itself revealed the hand of Hashem.

Summary: When Lavan and Besuel said "From Hashem the matter has come forth; we cannot speak to you bad or good," they spoke the literal truth. Though they were resha'im who would have wanted to obstruct the match, Hashem deprived them of the very ability to speak for or against it. Their forced inability to object is precisely how they recognized that the shidduch was decreed by Hashem.