I'm not sure I'm following.
I had a thread before purge that was about "Perseverance of the Saints."
It is a little different than OSAS in emphasis and concern. It isn't that A Calvinist doesn't believe that one saved remains saved (we do) but rather that we believe that a Christian is God's workmanship Ephesians 2:10 and that he/she is a new creation that will necessarily produce work in keeping with a new nature. 2 Corinthians 5:17
This doesn't mean that a new creation will grow immediately nor they will not have bumps in their life, but salvation is always by grace, through faith Ephesians 2:8,9 Romans 11:6
As far as John 3:15-20
Joh 3:15that whoever believes in him may have eternal life.
Joh 3:16"For God so loved the world, that he gave his only Son, that whoever believes in him should not perish but have eternal life.
Joh 3:17For God did not send his Son into the world to condemn the world, but in order that the world might be saved through him.
Joh 3:18Whoever believes in him is not condemned, but whoever does not believe is condemned already, because he has not believed in the name of the only Son of God.
Joh 3:19And this is the judgment: the light has come into the world, and people loved the darkness rather than the light because their works were evil.
Joh 3:20For everyone who does wicked things hates the light and does not come to the light, lest his works should be exposed.
Joh 3:21But whoever does what is true comes to the light, so that it may be clearly seen that his works have been carried out in God."
How does John 3:15-20 countermand OSAS? Or were you thinking of something else? Are you assuming Nicodemus, as a Pharisee/teacher, was 'saved?' :idunno: Not quite picking up where you are pointing.