If you don’t have a reason why you picked him, then you likely picked him just because you like the name. Be honest about that. You can also add though that St. Nathanael was one of the apostles, also known as St. Bartholomew (feast day: August 24). Of him, Jesus said:
Jesus saw Nathanael coming to him, and said of him, “Behold, an Israelite indeed, in whom is no guile!” (John 1:47).
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