In Romans 11:17-22 we are told about how gentiles are grafted into Israel to share in the blessings that God has promised through Abraham. Some think that it shows people being saved and then unsaved, so let's look at that passage and then review what it says.
Rom 11:17-22 But if some of the branches were broken off, and you, although a wild olive shoot, were grafted in among the others and now share in the nourishing root of the olive tree, do not be arrogant toward the branches. If you are, remember it is not you who support the root, but the root that supports you. Then you will say, "Branches were broken off so that I might be grafted in." That is true. They were broken off because of their unbelief, but you stand fast through faith. So do not become proud, but stand in awe. For if God did not spare the natural branches, neither will he spare you. Note then the kindness and the severity of God: severity toward those who have fallen, but God's kindness to you, provided you continue in his kindness. Otherwise you too will be cut off.
Roman's chapter 11 is an interesting passage of scripture and how one understand it hinges on whether one considers that gentiles have been grafted into places left in 'Physical Israel' when 'Physical Israelite' branches were cut off, or whether one considers that gentiles converts have been grafted into 'Spiritual Israel' when 'Jews' were cut off this cultivated olive tree. Obviously they have to be grafted into a suitable 'matching' place.
So, when are these Christians grafted in? Obviously they are grafted in
after accepting Jesus as Lord and Saviour. The question then is - Can
Spiritual Christians be grafted into a natural (carnal) olive tree?
Is Jesus the root of a carnal olive tree?
So all are treated the same! God, not being a respector of persons, gives all people the opportunity to put faith in His provision for eternal life.
We know from John 10:27-29 that once we give ourselves to Jesus Christ and place ourselves in his care by acepting his sacrifice on our behalf and making him our Lord and Saviour, then nothing can separate us from him, or shake us out of his hand.
John 10:27-29 “My sheep hear My voice, and I know them, and they follow Me; and I give unto them eternal life and they shall NEVER perish and no-one can snatch them out of my hand. My Father, who has given them to Me, is greater than all, and NO-ONE can snatch them out of My Father's hand.”
To me this and other similar scriptures makes the idea of being saved, then being lost, then saved, then lost again a non-starter, because it makes God seem like a catcher with 'butter-fingers'. He has you and gives you eternal life and salvation and then he loses you and has to take them away. Then He gets another chance and gives you eternal life again and salvation but can lose you again....! So one has to ask how 'eternal' is eternal life? And your answer applies to God also!In the first letter of John we learn this...
1Joh 5:11-13 And this is the testimony, that God gave us eternal life, and this life is in his Son. Whoever has the Son has life; whoever does not have the Son of God does not have life. I write these things to you who believe in the name of the Son of God that you may know that you have eternal life.
John tells us that believers who put their trust in Jesus are, as with John, 'given' eternal life. It's something they 'have' already. How long does eternity last for? If God can give it to you one day and take it away the next, just how trustworthy is He when He gives us gifts?
We all have to come to the point where we either accept or reject allegiance to Jesus. Do we follow the example of the demons who reject the sovereignty of Jesus or do we accept Christ's sovereignty, trust in him only, and receive salvation in Jesus Christ.
And to my understanding, once received always kept, as you live in Christ and grow in grace.
As children of Adam, our good deeds could not make us righteous;
the result of Adam's sin being so all encompassing.
Best wishes for Grace and the Peace of Jesus.