I recently began listening to a series by the White Horse Inn as they tackle the Sermont on the Mount.
The gentlemen discussed that the Sermon on the Mount is in many ways a retelling of the story of Moses.
Moses and the elders went up to Mt. Sinai to receive the Law from the LORD. The Law's basic framework stated "...if you do these things, you will live and be blessed. If you do not do these things, you will die and be cursed."
Moses was the covenant mediator between Yahweh and Israel.
Jesus is a better Mediator of a better covenant.
Jesus begins speaking the Good News of the Kingdom by speaking blessing upon His hearers. He is not simply flattering them with platitudes about "the silver lining" and "look on the bright side." He is not commanding people to be meek, to be thirsty, to be persecuted, to be poor in spirit. These are not new marching orders. These are blessings bestowed by God to the people of His choosing, upon whom He shows faithful love.
Most people read the beatitudes and have heard them preached as "be" attitudes. These are the things you should be. It is not inaccurate to say that these are desirable states of being and that our hearts should long to be meek, thirsty for righteous, poor in spirit, etc... However, if it is on us to become these things, then it is simply a new Law. Meet the new Law, same as the old Law.
In the Good News God provides that which he commands. The prayer of St. Augustine has been answered and the ability to perform and be that which God demands is fulfilled in Jesus.
This is the Good News of the Gospel.