Why does Israel advise Gentiles to become Noahide instead of converting?

First, let’s be clear — the modern State of Israel is not advising Gentiles, as a whole, to do anything. (Israel places various demands on Jews, and non-Jews, who are citizens or guests of the State of Israel. Israel places few, if any, demands on people outside of Israel.)

Using Israel in the older sense, as “the children of Israel” or “the people of Israel” — i.e. as a synonym for the Jewish people — is a more interesting question, and, I assume, is what was intended.

Jews don’t particularly advise Gentiles to become Noahide, i.e. to follow the seven Noahide commandments. Judaism simply explains that, according to Jewish belief, there are 613 commandments for Jews… but that if you are not Jewish; following the seven most basic commandments will still assure you of a place in the World to Come.

If you think about Judaism in terms of the “light unto the nations” concept — that, according to Jewish belief, God wanted people to behave morally, but understood that people need role models, and so he set up a group to be burdened with a higher standard — this makes sense.

The seven Noahide commandments, in case you were wondering, can be found in the Babylonian Talmud (Avodah Zarah 8:4, Sanhedrin 56a-b), and they are:

Do not worship idols.

Do not curse God.

Do not murder.

Do not commit adultery, bestiality, or sexual immorality.

Do not steal.

Do not eat flesh torn from a living animal.

Establish courts of justice.

So, if you are not Jewish, but you are okay with following those rules, then according to Judaism, you’re doing well.

If you don’t care how Judaism feels about you, then it doesn’t matter. You be you.