This is the idea of perseverance that Calvin mangles so badly. With the help of the Holy Spirit, we persevere. It’s not that we take the credit; it’s that if we stumble and fall and don’t get up, we will never finish the journey. If we are predestined to Heaven, then we don’t get the credit for going there.
If we refuse to go there, regardless of the Holy Spirit’s influence, then, we unelect ourselves. And at that point, unless we repent, confess our sins and ask pardon from God, we assume the status of what the Calvinists call the unelect.
The unelect can do no good in God’s eyes? Does that mean that if one practices the Beatitudes that one is automatically one of the elect?
What is the quantitative difference between elect sin and non elect sin?
All Calvin and the other Reformers said here is that after falling down, God does not leave His child lying in the dirt to die. God always picks His children up so that they WILL finish the journey. Does that sound so heretical? :)
The unelect can do no good in God’s eyes?
Correct. The unelect can do plenty that you and I would normally call "good", but to God it is as filthy rags. There is a timing element involved also. While the elect are technically elect for all time, they do not function as the elect, for these purposes, until the point of belief. Therefore, before I became a believer all of my deeds were worthless in God's eyes also, even though I am (I claim to be) of the elect. The non believer, elect or not, is incapable of doing anything in service to God, so it cannot be considered "good" in His eyes.
Does that mean that if one practices the Beatitudes that one is automatically one of the elect?
No, deeds do not make a person one of the elect. God predestinating makes a person one of the elect. The elect become aware they are of the elect when Holy Spirit regenerates them and they become believers.
What is the quantitative difference between elect sin and non elect sin?
Statistically, the elect should sin less often after regeneration. I presume that by the numbers a full Adamic nature sins more often than a Godly nature with a remnant.