en_tn_condensed/jud/01/04.md

For certain men have slipped in secretly among you

"For some men have come in among the believers without drawing attention to themselves"

men who were marked out for condemnation

This can also be put into the active voice. Alternate translation: "men whom God chose to condemn" (See: rc://en/ta/man/translate/figs-activepassive)

who have changed the grace of our God into sensuality

God's grace is spoken of as if it were a thing that could be changed into something horrible. Alternate translation: "who teach that God's grace permits one to continue to live in sexual sin" (See: rc://en/ta/man/translate/figs-metaphor)

deny our only Master and Lord, Jesus Christ

Possible meanings are 1) they teach that he is not God or 2) these men do not obey Jesus Christ.