“had not been clothed.” In this case, it is important to translate the text in a way that brings out the force of the verb in a way that provides the best understanding of the parable that Jesus is telling. The verb is a passive perfect participle. Although the form of the Greek verb is such that it can be read as either middle voice or passive voice, in this context it is best understood as a passive voice verb, showing that the man had not let himself be clothed in wedding clothes by the king’s attendant (cp. R. C. H. Lenski, The Interpretation of St. Matthew’s Gospel).
The parable is about the Kingdom of Heaven and being clothed with “wedding clothes,” that is, garments appropriate for being saved and being at the wedding banquet of the Lamb. But no one can clothe themselves with righteousness or salvation to the end that they have everlasting life. To have everlasting life and be at the wedding banquet of the Lamb, each person must let themselves be clothed by God in the garments of righteousness and salvation that He provides.