That's poetic language about himself, not a separate being dwelt within him. It's understood like this: "why am I cast down, O poor old me? Why do I feel so disquieted?" I don't think king David was born again in the Holy Spirit, even though he had a heart after God's own heart.
King David was anointed, and anointing happens in the spirit. So, when he goes through troubled times he is calling his soul to praise God. In other words, he is trying to encourage himself by means of praising God.
You don't know that. Holy Spirit usually descended upon the individual at baptism. Whether he was born again or not, he was not talking to a separate being taken possession of him.
By trusting in the Person, atoning death, and resurrection of Jesus Christ.
If you don't believe in these three avenues of getting saved, then you'll remain confused by the three ways in which we receive salvation.
Spirit cannot be "dead", there's no such thing as "spiritual death". WHat's often taught as "spiritual death" is Adam and Eve's broken relationship with God, the exile from Eden disconnected them from God. In Rev. 20, it is the disobedient spirits that are condemned to suffer in the lake of fire for eternity.
Do those three operate independently? No. Does Scripture specify that any of those three relates to "saving" a specific component of the human being? No.
You are right when you say that the death of the spirit is disconnection from God. So, since their spirit cannot lead them anymore, who is the alternative? It's the soul.
No. They were saved by their faith just as Abraham was. So, the for the OT saints, it really does not matter much about knowing the tripartite nature of man. However, it is very much for us as NT believers to know this distinction because Satan attacks in our soul i.e. our mind, emotions, and will. For this reason, we need discerning through our spirit.
The first two happens together as we pray the prayer of repentance and salvation. The third one happens as we take water baptism. I am relating this to what is said in 1 Thes. 5:23 that we should keep our spirit, soul, and body blameless at the coming of our Lord Jesus Christ.
That verse tells us clearly that we are tripartite beings. It does not say anything about distinct "methods" for salvation for each part. It also puts the onus on us to "keep... blameless", which is not "save".
No. They were saved by grace through faith.
Once a person is born again, the onus definitely is on us because we have a free will. God's grace only assists us as we pursue God.
Grace and faith is definitely from God. Exercising the free will to accept that grace is our part.
Grace is the exercise of God's power in/on/through an individual. The exercise of God's power is independent from and incidental to any response of an individual.
Eph. 2:8-9 says, "For by grace are ye saved through faith; and that not of yourselves: it is the gift of God: Not of works, lest any man should boast.". God gives us the gift of faith. Using this faith, we believe the gospel, call upon the name of the Lord and will be saved. When it says, "not of yourselves", it means our salvation was not based on our merit but purely because of the grace of God.
