Tafsir of Al-Qalam 68:24

The particle an (that) is explanatory of the meaning of speech contained within the word yatakhāfatūn (whispering/muttering), or it is masdariyyah (serving as an infinitive marker), in which case the estimation is bi-an (by the fact that). The first interpretation is supported by the reading of ‘Abdullah and Ibn Abi ‘Ablah, who omitted it. Based on this, it is said that it follows an implied verb of speech. It is also said that the operative factor governing it is yatakhāfatūn itself, due to its inclusion of the meaning of speech—this being the Kufan school of thought regarding it and its likes.

Regardless of the interpretation, the intention behind forbidding the poor person from entering is to emphasize the prohibition against allowing him access to it, similar to the saying, "I will not see you here" (meaning: do not let me see you here).