Third-Isaiah, Paul and Mark are concerned with God entering our lives in a unique way -- something around which the coming celebration of Christmas revolves. Yet each writer has his own unique place in salvation history, outside the context of that specific, 2,000-years-ago Bethlehem event.
Third-Isaiah, for instance, is addressing Israelites recently freed from their 50-year Babylonian exile. Though the prophet encourages his people to return to the Promised Land, he's convinced that rebuilding physical structures only makes sense after someone is first committed to rebuilding a relationship with Yahweh. No one will notice God breaking into their lives until they first become the people of God.
Awareness of God's actions in our lives is also at the heart of today's 1 Corinthians pericope.