Becoming a child of God is not equivalent to being saved. A child can disown his inheritance. I agree that once one is saved, one is always saved. But the Apostles taught that one is not saved until they have finished the race, fought the good fight, and kept the faith. The notion that one is saved at one point in time for all time is a recent innovation - what the Apostles would call “a different gospel”.
“Not that I have already obtained this or have already reached the goal; but I press on to make it my own, because Christ Jesus has made me his own. 13 Beloved, I do not consider that I have made it my own; but this one thing I do: forgetting what lies behind and straining forward to what lies ahead, 14 I press on toward the goal for the prize of the heavenly call of God in Christ Jesus. 15 Let those of us then who are mature be of the same mind; and if you think differently about anything, this too God will reveal to you. 16 Only let us hold fast to what we have attained.” Phil 3:12-16
Why does Paul say it is more “mature” not to have an OSAS attitude? Why strain forward, if you have already arrived? Why “press on” if one has already reached the goal?
You are assuming that, because God loves someone, He will not let them walk away from Him. Even a cursory reading of scripture clearly shows that God loves those whom He has chosen, but He still lets them walk away from Him. He will never stop loving us, even as we pass thru the gates of hell.
Mark 10:21-22
21 Jesus, looking at him, loved him and said, “You lack one thing; go, sell what you own, and give the money to the poor, and you will have treasure in heaven; then come, follow me.” 22 When he heard this, he was shocked and went away grieving, for he had many possessions.
I am sure that Jesus was grieving too, since that what happens when someone you love does something self injurious.