Sufficiency vs. Necessity
The central difference between Reformed and non-Reformed theology is that the former affirms that Jesus Christ is SUFFICIENT to save to the uttermost while later believes that while Jesus is NECESSARY, but He is NOT SUFFICIENT. The Reformers never charged Rome of believing one could be saved apart from grace. That wasn't the debate. The debate of the Reformation was never ever about the necessity of grace, it was about the sufficiency of grace. Reformed Theology emphasizes more than anything else, the sufficiency of Christ in salvation. There is nothing more essential to its position and this is what sets it apart from other all other theologies.
The word "sufficient", in this case, means that Jesus Christ meets all the conditions for us that are necessary for our salvation, not only some of the conditions. It further means what Jesus does for us on the cross meets all of God's requirements for us, including giving us the new heart which is needed to believe and obey (Ezekiel 36:26).
Evangelicalism broadly believes in an insufficient Jesus whose love is conditional, that is, that we must first meet a condition if He will help/love us. Can you imagine a parent who saw their toddler run out into traffic and first required them to meet a condition before the parent would run out to save them from oncoming traffic? No, no, no... parental love is unconditional and would run out at the risk of their life to save the child regardless of the child's will at the time because the parent loves his child and knows better than the child what is good for him/her. If this is true about love in everyday life, how much more is it true of God. No person would say that the parent who required the child to first meet a condition was more loving. That is why the argument about the necessity of free will to have true love is fallacious. In the Bible, God gives conditions, but in Jesus He meets all the conditions for us.
“God knows we have nothing of ourselves, therefore in the covenant of grace he requires no more than he gives, but gives what he requires, and accepts what he gives.”
― Richard Sibbes, The Bruised Reed