Fat Tuesday, then, is the last day before the time of suffering and deprivation. In other words, it is the last chance to indulge one’s desire before depriving oneself. This is where the concept of “fat” comes in; indulgence. This is not only food indulgences, but all sorts of “fleshly” indulgences (i.e., sex). It means giving into all desires. This is where the term “Carnaval” comes it. It links up to the Latin that our English word “carnal” comes from (i.e. flesh). Literally, “Carnaval” means “flesh party”.
The sad part about this is that while a time of fasting is certainly pious, the logic of Mardi Gras is entirely unbiblical. But how?
Paul and Jesus both taught that being a Christian was equivalent to New Birth (John 3:3). What does he mean by this? It means that becoming a Christian means that the sinful nature (i.e. destructive human desires) is put to death and a new self is born. In other words, destructive human desires no longer control us.
Paul says it best with this:
What shall we say then? Are we to continue in sin that grace may abound? By no means! How can we who died to sin still live in it? Do you not know that all of us who have been baptized into Christ Jesus were baptized into his death? We were buried therefore with him by baptism into death, in order that, just as Christ was raised from the dead by the glory of the Father, we too might walk in newness of life.
For if we have been united with him in a death like his, we shall certainly be united with him in a resurrection like his. We know that our old self was crucified with him in order that the body of sin might be brought to nothing, so that we would no longer be enslaved to sin. For one who has died has been set free from sin. Now if we have died with Christ, we believe that we will also live with him. We know that Christ, being raised from the dead, will never die again; death no longer has dominion over him. For the death he died he died to sin, once for all, but the life he lives he lives to God. 11 So you also must consider yourselves dead to sin and alive to God in Christ Jesus.
Let not sin therefore reign in your mortal body, to make you obey its passions. Do not present your members to sin as instruments for unrighteousness, but present yourselves to God as those who have been brought from death to life, and your members to God as instruments for righteousness (Romans 6:1–13, ESV).