A) Due to the six year term senators have some insulation from short term political will and can take a longer term view on important issues. They are not constantly engaged in campaigning so they are better able to focus on legislation. These longer terms also lend themselves to fuller development of relationships with their peers which may prove useful in reaching consensus on tough issues.
B) The framers considered the Senate to be the deliberative body of congress and used term length as a framework to support that end.
