Do you believe in purgatory and where is that concept seen in scripture?Yes, I most certainly believe in Purgatory. It will be helpful at the onset to define exactly what Catholics believe about it. For this, read articles 1030-1032 from the Catechism.
Now, the logic behind it is this: we have a faulty human nature that causes us to sin, predisposes us to sin, and accounts for our inclination to sin even after we have been "saved" by Jesus Christ. "I do not understand my own actions. For I do not do what I want, but I do the very thing I hate" (Rom 7:15). This quality of our human nature, what we call concupiscence (kon-KYOO-pi-sints), is an imperfection that is always with us.
We also know that some sins have a mortal effect and some do not. "All wrongdoing is sin, but there is sin which is not mortal" (1 Jn 5:17). Catholics call these non-mortal sins "venial sins" (cf. CCC, #1854-1864). Thus, the possibility exists that we can die with these venial sins on our soul and still go to heaven, since these sins are not of the type that have a mortal effect on our relationship with God.
Thirdly, we know that sin has an effect both on our relationship with God and our relationship with man. "We, though many, are one body in Christ, and individually members one of another" (Rom 12:5). "If one member suffers, all suffer together; if one member is honored, all rejoice together" (1 Cor 12:26). The Lord forgave David for killing Bathsheba's husband and assured David that he would not die, but his son still had to be taken from him (2 Sam 12:13-14). We must renew friendship with our fellow man before we meet the Judge (Mt 5:25).
Finally, and most importantly, we know that nothing unclean shall enter heaven (Rev 21:27). Without holiness, no one shall see the Lord (Heb 12:14). When we die, we bring with us our faulty human natures, any venial sins we have committed, and responsibility for whatever harm we have done to the Body of Christ that we have not remedied in this life. Although we may have rectified the divine effect of our sin through repentence (in which case heaven is our just reward), if we have not rectified the human effect of our sin, this must take place before we can enter heaven. "Make friends quickly with your accuser, while you are going with him to court, lest your accuser hand you over to the judge, and the judge to the guard, and you be put in prison; truly, I say to you, you will never get out till you have paid the last penny" (Mt 5:25-26). Likewise, our human natures must be restored and any venial sins must be purged. These are all imperfections of our soul, and we cannot enter heaven as long as they persist.
We are everyday working out our faith with fear and trembling (Phil 2:12), we are everyday "being saved" (1 Cor 1:18; 2 Cor 2:15). Yet, often times, this life-long process of sanctification does not end with our death. Before a soul enters heaven, it is often necessary of the Lord to make one final act of sanctification. This final act is called Purgatory.
Now that I have stated why purification in the afterlife may be necessary, it is left only to show that the reality of Purgaotry is attested to by Scripture. This will come in a subsequent post.