The crucifix is the constant reminder that the crucifixion was an historical event that cannot be denied, that while we were yet sinners Christ died for us, that we have been crucified with him and risen with him in baptism, and as a bulwark against making Christ into a feel-good guy who only meant to be nice instead of the Lamb of God who came to sacrifice himself for our sake, to satisfy God’s justice. Here are verses that speak to these things:
Acts.2 this Jesus, delivered up according to the definite plan and foreknowledge of God, you crucified and killed by the hands of lawless men.  Let all the house of Israel therefore know assuredly that God has made him both Lord and Christ, this Jesus whom you crucified."
Acts.4 be it known to you all, and to all the people of Israel, that by the name of Jesus Christ of Nazareth, whom you crucified, whom God raised from the dead, by him this man is standing before you well.
Rom.6 We know that our old self was crucified with him so that the sinful body might be destroyed, and we might no longer be enslaved to sin.
1Cor.1 but we preach Christ crucified, a stumbling block to Jews and folly to Gentiles,
1Cor.2 For I decided to know nothing among you except Jesus Christ and him crucified.  None of the rulers of this age understood this; for if they had, they would not have crucified the Lord of glory.
2Cor.13 For he was crucified in weakness, but lives by the power of God. For we are weak in him, but in dealing with you we shall live with him by the power of God.
Gal.2 I have been crucified with Christ; it is no longer I who live, but Christ who lives in me; and the life I now live in the flesh I live by faith in the Son of God, who loved me and gave himself for me.
Gal.3 O foolish Galatians! Who has bewitched you, before whose eyes Jesus Christ was publicly portrayed as crucified?
Gal.5 And those who belong to Christ Jesus have crucified the flesh with its passions and desires.
Gal.6 But far be it from me to glory except in the cross of our Lord Jesus Christ, by which the world has been crucified to me, and I to the world.