That is a lot of questions. It will probably take several post to answer them, and I’m not a theologian or expert. A simple lay person doing my best to understand.
So, who truly knows who has a good heart bearing fruit out of good soil?
I take this question to mean, how can we know that we are one of the ones “Given to Christ by the Father”.
My answer is that it is a two fold process. One is internal and personal and the other is external and evidentiary.
First the internal. Which is the indwelling Spirit, which we believe is given at conversion, we do not hold that Baptism automatically gives the Holy Spirit to a person. When we receive the Spirit is another topic that I will not get into here. The key point is the Spirit gives our hearts witness that we are indeed Children of God. This can be seen in several passages.
Romans 8:16.
The Spirit himself bears witness with our spirit that we are children of God
Romans 5:5
Now hope does not disappoint, because the love of God has been poured out in our hearts by the Holy Spirit who was given to us
Galatians 4: 6
And because you are sons, God has sent forth the Spirit of His Son into your hearts
1 John 4:13
By this we know that we abide in him and he in us, because he has given us of his Spirit.
I could go on but you get the idea. The first way we know we are indeed “Children of God” is because of the testimony and work of the Holy Spirit in our hearts.
The second way we know we are children of God is because we have been changed. Our affections are changed and as a result our actions are changed. This change in heart (by the Holy Spirit) is what causes us to repent of sin, confess our sins to one another, love our neighbor, help those in need and so forth.
It seems that there are two ways we can be deceived. One is, “I’ve prayed and prayer and ask God to forgive me and now I’m a Christian”. And the other is "I’m following the rules and doing what my preacher/priest says and doing my best to be a good person, therefore I’m a Christian.
From the way I see it, both of those are faulty reasoning. We can pray and ask for forgiveness all day long, but if our heart isn’t changed and our lives aren’t different then we are fooling ourselves into believe we are a Christian.
We can also follow the “rules” and do our best to be righteous and holy, but without a heart change we are still fooling ourselves. That turns the Gospel from good news to good advice. When end up trying to save ourselves by our righteousness instead of relying on Christ and what he has done to save us.
1 John 5:13 says
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.
In 1 John you see the evidence and how we can know we have eternal life as being both Spiritual evidence as in 1 John 4:13 and external evidence as in 1 John 4 :7.
We know we have eternal life when the Spirit gives witness to our spirit that we are children of God and when that Spirit produces fruit in our life. If both of those things aren’t happening then we should question our status.