This is the symbolic preparation before something new is embarked upon. You stop for a moment and clean your shoes so that what is unwanted from your past will not be carried forward into your future. Also consider that a doormat is sometimes used as a term for a person who allows other people to wipe their feet on them figuratively, and this meaning may be reflected in a dream.
[1]To dream about a Welcome Mat is a positive dream, foretelling that you will be distinguished amongst your social circle.
If the doormat in your dream is blank, disappointments may be in store for you.
[2]You are feeling inferior or stepped on. Everything dirty seems to be unloaded on you.
[3]Indication that one is being used as a doormat
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