I’m a Christian who was raised in a Christian household, but recently my family learned that my father (who was adopted) is 100% Jewish. Does that make me Jewish too?
Regarding your possible Jewish identity, we do not believe you are Jewish according to the Biblical definition. In the Bible, Jewishness is a combination of two things: bloodline and covenant-keeping observances (called mitzvot).
First, a Jew is determined by bloodline. Biblically, a Jew is descended from Abraham, Isaac and Jacob, and that bloodline is traced through the father, so if a person’s father is Jewish, then the child is Jewish. After the destruction of the Jewish temple, the rabbis switched to tracing Jewishness through the mother rather than the father, nevertheless the Biblical method remains to trace through the father. So according to your bloodline, you could qualify as Jewish.
On the other hand, Jewishness also requires observance of covenant-keeping practices like circumcision, keeping Sabbath, observing feasts, Torah study, etc. If a person has not engaged in these practices routinely, then the person is not Jewish. The Bible demands these observances or else a person is cut off from Israel:
Gen. 17:14 “But an uncircumcised male who is not circumcised in the flesh of his foreskin, that person shall be cut off from his people; he has broken My covenant.”
Ex. 12:18 ‘In the first month, on the fourteenth day of the month at evening, you shall eat unleavened bread, until the twenty-first day of the month at evening.
Ex. 12:19 ‘Seven days there shall be no leaven found in your houses; for whoever eats what is leavened, that person shall be cut off from the congregation of Israel, whether he is an alien or a native of the land.
Ex. 31:14 ‘Therefore you are to observe the sabbath, for it is holy to you. Everyone who profanes it shall surely be put to death; for whoever does any work on it, that person shall be cut off from among his people.
Since you say you grew up in a Christian home, then we assume you did not practice mitzvot consistently, which means you are not considered Jewish according to the Bible. You are a Gentile.
Furthermore, in the Church there is no distinction between Jew and Gentile (Galatians 3:28), so there is no benefit in one identity over another. For a Christian, being counted Jewish (or not) is meaningless.