I love the two-sided Gospel in Romans 3 and 5.
First, the cross demonstrates the righteousness of God (Rom. 3.23-26). What Paul argues in that text is that God would be unrighteous if He were just to let sin slide. If it could go on without punishment, it's no big deal to Him. Furthermore, if He justifies sinners then He obviously is unrighteous because who wants to be on the side of the Judge that declares clearly guilty offenders to be innocent before Him?
That's where Jesus the Propitiation comes in. Propitiation means that God's wrath is satisfied by the sacrifice of Christ and God's favor is inclined toward us. It's both removal of guilt and release of favor. With sin punished, God is no longer guilty of unrighteousness. An amazing solution to a complex problem.
And that's just the legal side.
Second, the cross displays God's love (Rom. 5.8). It's not enough for us to be legally right before Him. Because of His love we are relationally right as well. He has drawn us in, adopting us into His family, making us heirs with Christ. This broad, long, high, and deep love is the kind of covenant love that God has for His people from the beginning. It precedes any love that we might have for Him and actually causes the love we have for Him. His love motivated Him to rescue us and, for many, has been His conquering force in their lives.
So we're legally justified before God and relationally adopted by Him.
That's why the Good News is so good.
But that's just me thinking thoughts...