It is good that those who believe that "Once saved are not saved forever" are careful in their conduct. They show some verses in support. They can only caution and encourage others in the light of the verses. They have no right to doubt or judge other person's salvation. It is true that Israelites were punished but all their punishment was earthly. Moses did not enter the promised land. But you see him in Heb 11. We too may be removed from the earth if we don't deserve our stay here.(Ananiah and Sapphira). Overall understanding of Scripture helps us. Not verses. Verses should be understood in the context of the overriding truth. We are born from above. Once born can never be unborn. Salvation is a gift. Gift is not taken back- even Spiritual gift. (Rom 11:29). We are in the double fisted protection of the Father and the Son. He gave us "Eternal Life". (John 10: 27 to 29). We are chosen (John 6:37,39 to 40). For us it is impossible. But for God? (Matt 19:26). How much time does a dying sinner take for showing repentance?
God may give a chance. What about Samson? Don't you find him in Hebrews 11? Let us learn to be kind. (Gal 6:1;James 5:19,20; Jude 22to25 and Hebrews 12:12).
Let us learn to walk in the light confessing known sins and seeking forgiveness. Unknown sins(because our eyes haven't fallen on those portions of Scripture) He will take care of. Sin should be disgusting to us. May the Father help us through the Spirit He put in us by causing in us such disgust and may He help us to come out of it as we keep seeking and cooperating.
Let us help people who are yet to be saved by making them come to the true knowledge of the Cross and it's implications. May God grant us his help to do so.