Hebrews 10: 38-39 But the just shall live by faith; and if he draws back and shrinks in fear, My soul has no delight or pleasure in him. 39 But our way is not that of those who draw back to eternal misery (perdition) and are utterly destroyed, but we are of those who believe [who cleave to and trust in and rely on God through Jesus Christ, the Messiah] and by faith preserve the soul.
Faith is not a magic spell neither an ability to keep the laws written on a moral code given by God. Hebrews 10 says Faith is to believe Christ took away our sin at the cross. His work made us perfect, holy and it cleansed us from an evil conscience. Let's break the chapter down from start to finish:
Faith is to believe Christ's sacrifice is superior to the sacrifices offered in the old covenant. Therefore, his sacrifice made us completely perfect. It cleansed us. It took away our guilt, consciousness of sin, and sin.
Hebrews 10: 1- 4 For since the Law has merely a rude outline (foreshadowing) of the good things to come—instead of fully expressing those things—it can never by offering the same sacrifices continually year after year make perfect those who approach [its altars]. 2 For if it were otherwise, would [these sacrifices] not have stopped being offered? Since the worshipers had once for all been cleansed, they would no longer have any guilt or consciousness of sin. 3 But [as it is] these sacrifices annually bring a fresh remembrance of sins [to be atoned for], 4 Because the blood of bulls and goats is powerless to take sins away.
Faith is to believe Jesus came to do God's will, which is: "Jesus MADE US holy THROUGH HIS sacrifice." (Made past tense. It has been done!)
Hebrews 10: 9-10 He then went on to say, Behold, [here] I am, coming to do Your will. Thus He does away with and annuls the first (former) order [as a means of expiating sin] so that He might inaugurate and establish the second (latter) order. 10 And in accordance with this will [of God], we have been made holy (consecrated and sanctified) through the offering made once for all of the body of Jesus Christ (the Anointed One).