As ambassadors selected by the state legislatures, each sovereign state government has equal representation to discuss national matters. This was set up differently from the House, where Representatives are elected by the people at the district level, and more populous states had more Representatives.
The 17th amendment changed the role of Senators from ambassadors to super-Representatives, since they were no longer directly appointed by the legislatures with the intent on representing their state's long-term needs to the other states (hence their six-year terms).
The vertical alignment of people -> state legislature -> Senators was broken. We now have:
The state governments themselves have been outflanked by the federal government and no longer have a direct participation in the federation of states. The 17th amendment took that away.
-PJ