The passage from Romans is both clear and powerful, and it only needs reflection and prayer rather any commentary that I might provide.  Precisely because it is so clear, I would like to address instead the psalm and the response we include in today's liturgy: "If today you hear his voice, harden not your hearts."

"If" is the problematic word here: "when" would be better, but best (I think) would be something like "when you actually pay attention what the Lord is saying to you."

The Samaritan Woman, one of the many feisty people whom John describes in his portrayal of the Christ whom he had encountered, is quick to hear what Jesus has to say and to engage him in conversation on the deepest level: he challenges her and she ups his ante, challenging him in return: they quickly arrive at the most important questions about who Jesus is, who she is, and what it means for her.

Jesus wants us to come to grips with his questions, his challenges, his invitations to a deeper understanding (both of him and of ourselves) and love.  That can mean that we struggle with intellectual questions and moral problems, but when it comes down to it we must, like the Samaritan Woman, admit that we are sinners and in need of revival, forgiveness, healing, re-creation.

Hardening our hearts is the spiritual equivalent of a two-year-old's pout, a refusal to be loved and given life.  Do we trust our Father's call?  Can we abandon ourselves to the invitations of the Spirit?  Can we indeed forget our petty personal fixations to "acclaim the Rock of our salvation," "to greet him with thanksgiving," and all the rest that the psalm proposes?