אֵֽרֲדָה־נָּ֣א וְאֶרְאֶ֔ה הַכְּצַעֲקָתָ֛הּ הַבָּ֥אָה אֵלַ֖י עָשׂ֣וּ ׀ כָּלָ֑ה וְאִם־לֹ֖א אֵדָֽעָה׃
I will go down now, and see whether they have done altogether according to the cry of it, which is come unto Me; and if not, I will know.’
Rashi on Genesis
ארדה נא I WILL GO DOWN NOW — This teaches the judges that they should not give decisions in cases involving capital punishment, except after having carefully looked into the matter — all as I have explained in the section dealing with the dispersion of the nations (11:5). Another explanation of ארדה נא is: I will go down to the very end of their doings (I will fathom the depths of their wickedness).
Rashbam on Genesis
עשו כלה, the vertical line after the word עשו is like a comma between these words, i.e. “if they have done as reported, I will put an end to them.”
Sforno on Genesis
I will descend now. I will plumb the depths of their wickedness to see what will come of it in the end.