There are so many scriptures that say that if we belong to Christ, our flesh (sin nature) has been crucified with Christ and is dead - and we rise in the Spirit, with a new nature. And yet you say this isn't true. What scriptures say we, as Christians, still have a sin nature? You said, "Everyone struggles with there sin, because one has to master ones self, that's self control." Willpower is not the same as "by the Spirit." There is no struggle in the Spirit - He did all the heavy lifting when he empowered us to not sin.
Romans 6:1-7
What shall we say then? Shall we continue in sin that grace may abound? 2 Certainly not! How shall we who died to sin live any longer in it? 3 Or do you not know that as many of us as were baptized into Christ Jesus were baptized into His death? 4 Therefore we were buried with Him through baptism into death, that just as Christ was raised from the dead by the glory of the Father, even so we also should walk in newness of life. 5 For if we have been united together in the likeness of His death, certainly we also shall be in the likeness of His resurrection, 6 knowing this, that our old man was crucified with Him, that the body of sin might be done away with, that we should no longer be slaves of sin. 7 For he who has died has been freed from sin.
Romans 8:1-9 There is therefore now no condemnation to those who are in Christ Jesus, who do not walk according to the flesh, but according to the Spirit. 2 For the law of the Spirit of life in Christ Jesus has made me free from the law of sin and death. 3 For what the law could not do in that it was weak through the flesh, God did by sending His own Son in the likeness of sinful flesh, on account of sin: He condemned sin in the flesh, 4 that the righteous requirement of the law might be fulfilled in us who do not walk according to the flesh but according to the Spirit. 5 For those who live according to the flesh set their minds on the things of the flesh, but those who live according to the Spirit, the things of the Spirit. 6 For to be carnally minded is death, but to be spiritually minded is life and peace. 7 Because the carnal mind is enmity against God; for it is not subject to the law of God, nor indeed can be. 8 So then, those who are in the flesh cannot please God.
9 But you are not in the flesh but in the Spirit, if indeed the Spirit of God dwells in you. Now if anyone does not have the Spirit of Christ, he is not His.
John 8:34-36 Jesus answered them, “Most assuredly, I say to you, whoever commits sin is a slave of sin. 35 And a slave does not abide in the house forever, but a son abides forever. 36 Therefore if the Son makes you free, you shall be free indeed.
1 John 3:4-9 Whoever commits sin also commits lawlessness, and sin is lawlessness. 5 And you know that He was manifested to take away our sins, and in Him there is no sin. 6 Whoever abides in Him does not sin. Whoever sins has neither seen Him nor known Him. 7 Little children, let no one deceive you. He who practices righteousness is righteous, just as He is righteous. 8 He who sins is of the devil, for the devil has sinned from the beginning. For this purpose the Son of God was manifested, that He might destroy the works of the devil. 9 Whoever has been born of God does not sin, for His seed remains in him; and he cannot sin, because he has been born of God.