Yes it is necessary for conversion, and yes it is the work of God.
Man is active in conversion, that is the regenerate man, he is active even though hes being acted upon by God. Its like when Paul said Phil 2:12-13
12 Wherefore, my beloved, as ye have always obeyed, not as in my presence only, but now much more in my absence, work out your own salvation with fear and trembling.
13 For it is God which worketh in you both to will and to do of his good pleasure.
To say the renewed man isnt active in conversion lacks understanding. God causes him to be active Ezk 36:27
27 And I will put my spirit within you, and cause you to walk in my statutes, and ye shall keep my judgments, and do them.
Yes, God is the cause of salvation in all its parts.
Saul is writing to Jewish Christians at Philippi who are already saved.
And Ezekiel:
25 Then will
I sprinkle clean water upon you, and ye shall be clean: from all your filthiness, and from all your idols, will
I cleanse you.
26 A new heart also will
I give you, and fa new spirit will
I put within you: and
I will take away the stony heart out of your flesh, and
I will give you an heart of flesh.
27 And
I will put my spirit within you, and cause you to walk in my statutes, and ye shall keep my judgments, and do them. Eze. 36:25–27.
Remember Lucifer's 5 "
I wills"? (I will ascend into heaven, I will sit upon..."?)
God has 7 "I wills."
Not only is God the first cause in salvation and brings all that accompanies it, He is also directly involved in keeping a person saved and from falling. Totally. Finally. Eternally.
24 Now unto him that is able to keep you from falling, and to present you faultless before the presence of his glory with exceeding joy, Jude vs. 24.
If God does nothing men die in sin and eternally separated from Him.
Men (and women) are dead before Him. Even physically "alive" men are dead before Him.
What did Jesus say to "alive" dead people?
10
The thief [sin] cometh not, but for to steal, and to kill, and to destroy: I am come that they might have life, and that they might have it more abundantly. Jn 10:10.
And again, speaking to "alive" dead people:
24
Verily, verily, I say unto you, He that heareth my word, and believeth on him that sent me, hath everlasting life, and shall not come into condemnation; but is passed from death unto life. Jn 5:24.
Mankind has been infused with a false notion and belief since creation that we are alive, but we are not. We are merely animated. What's the term? "Dead man walking"?
God is alive. He defines life and living. He is the standard by which life and living is not only defined but judged against.
4 In him was life; and the life was the light of men. Jn 1:4.
It doesn't say, "and the life was the
life of men."
God is life. If our present existence is life, why is it necessary for God to take life from us? Why and how does sin kill life, especially if God breathed His life in man's nostrils?
Life cannot kill life. The Father cannot kill the Son. There is no such thing as deicide. Logos did not die on the cross. One cannot kill God. Jesus the man died on the cross. Sin cannot kill God, but it can kill man. It kills man because man is only animated. It mars and eventually destroys the animation God breathed into the nostrils of man. Since God is life and sin cannot kill God who is life, and if one thinks man when created became alive as God is alive how can sin kill the Deific Nature of life of God in man if indeed God breathed into man's nostrils His very own Deific life-nature? This ties in with my belief that God created man sinful.
Now, having said all that, salvation is the saving of man. If God breathed into the nostrils of man His very own Nature of His very own life, then sin could not kill man and man would not die. But man does die. Sin cannot kill God. Sin cannot kill any aspect of Deity. Sin cannot kill life, especially God's life. Man possessed nothing redeemable. Nothing. Not even faith. It was Christ's Faith that God honored and by which we are saved. God accepteth no man’s person (Gal. 2:6.)
16 Knowing that a man is not justified by the works of the law,
but by the faith of Jesus Christ, even we have believed in Jesus Christ, that we might be
justified by the faith of Christ, Gal. 2:16.
But it is the Faith of Christ He had towards His Father and THEN
in salvation is imparted to us that we might believe. Before that, we are as Lazarus, dead to God and dead without life.
We might be able to attempt to understand the 'ordo salutis' or the order of salvation, but every aspect of salvation is and comes from God. Man possessed none of what God brings to the table in the salvation of man. The only 'thing' needed for salvation is God. Repentance comes with salvation. Conversion comes with salvation. Justification comes with salvation. Righteousness comes with salvation. When God saves (salvation) a person everything comes from God towards that person's redemption. All these add-ons that this or that is NEEDED before we are salved comes from a man-centered theology, that I participated in my salvation, or God could not save me unless I allow it. No. God is not making things up as He goes along. He is actively and directly involved and it the first cause in man's salvation. It is a plan He initiated in Himself BEFORE He created heaven, earth and man. He wrote names in a book of life of the lamb before He created anything. All He is doing is following His pre-creation plan and saving individuals at their appointed time. Nothing is needed in order to be saved.
Only God. Salvation -
and all its parts - is of the LORD (Jonah 2:9.)