For a Catholic, to have faith is more than just a belief. It's our response to God (CCC 26). By faith, man completely submits his intellect and will to God. (CCC 143).
In essence, to have faith is to be completely obedient to God per Scripture. Christ tells us that if we love Him we will keep His commandments. If we love Him, we will have faith in Him and we will be obedient to Him. That's what faith is.
So, when He says something like, "Go, therefore and make disciples of all nations, baptizing them in the name of the Father, and of the Son, and of the Holy Spirit," (Matthew 28:19) We are obedient and baptize all disciples.
In Baptism, we are reborn into Christ. Per John 3:5, we are reborn with water and the Spirit. We are stripped of our sinful selves and reborn clean. The grace we receive unites us to Christ and strips us of our sins.
In Baptism, Paul tells us in Colossians that we were circumcised with a circumcision not administered by hand, stripping off our carnal body. (Colossians 2:11).
He also tells us in Romans that we were Baptized into His death so that we may rise with Him in the Resurrection. (Romans 6:3-5)
John the Baptist explains that with Christ's baptism we will be like wheat where our sinful chaff will be separated from us by His winnowing fork (Matthew 3:11-13) where the chaff will be burned away by fire.
And Peter tells us that Baptism is what saves us (1 Peter 3:21).
So, per Scripture, it is evident that Baptism is necessary and essential per Jesus Christ, John the Baptist, Peter, and Paul.