The Holy Spirit makes sanctification possible. We know that we cannot get to heaven on our
own—we need help to get there. Justification is a very important concept to understand.
What did justification, through an indwelling of the Holy Spirit, do for us?
Paragraph 1987 of CCC:
1987 The grace of the Holy Spirit has the power to justify us, that is, to cleanse us from our sins and to communicate to us “the righteousness of God through faith in Jesus Christ” and through Baptism.
Catholic Church. (1997). Catechism of the Catholic Church (2nd Ed., p. 481). Vatican City: Libreria Editrice Vaticana.
When we do something wrong, that small voice that complains can be from the Holy Spirit. This is how the Holy Spirit cleanses us.
Romans 6:8-11 says:
But if we have died with Christ, we believe that we shall also live with him. For we know that Christ being raised from the dead will never die again; death no longer has dominion over him. The death he died he died to sin, once for all, but the life he lives he lives to God. So you also must consider yourselves as dead to sin and alive to God in Christ Jesus