"And he said to them" (Exodus 19:25): he told them immediately and did not delay. Another interpretation: "And he said to them," he said to them, Receive the kingdom of Heaven with joy. Another interpretation: he said to them, Be those who say of yes, yes, and of no, no.
Receive the Kingdom of Heaven With Joy and Speak Plainly
Yalkut Shimoni on Torah 285:3
(שמות יט כה) וַיֹּאמֶר אֲלֵהֶם אָמַר לָהֶם מִיָּד וְלֹא עִכֵּב. דָּבָר אַחֵר וַיֹּאמֶר אֲלֵהֶם אָמַר לָהֶם הֱווּ מְקַבְּלִין מַלְכוּת שָׁמַיִם בְּשִׂמְחָה. דָּבָר אַחֵר אָמַר לָהֶם הֱיוּ אוֹמְרִים עַל הֵן הֵן וְעַל לָאו לָאו.