I want to know why Allaah is swearing by himself, Surah: 70 Ayah: 40. And I want to know if wearing shoes is Haraam?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.

Allaah, the Exalted, can swear by Himself, or swear with whatever He wishes from His Creation. It is wrong to say why Allaah swears by Himself. Allaah Says (what means): {He is not questioned about what He does, but they will be questioned.}[Quran 21:23].

As regards the second part of your question, it is not clear, however, what we may say is that it is permissible to wear shoes. Allaah Says (what means): {Say, “Who has forbidden the adornment of [i.e. from] Allah which He has produced for His servants and the good [lawful] things of provision?”}[Quran 7:32]. Therefore, it is permissible to wear shoes unless there is an extraordinary objection.

Allaah Knows best.