‘Hold something‘ とは、文字通り、手で何かをしっかり握っている、ということです。
‘Hold to something‘ とは、約束した事、やると決めた事柄を成し遂げるという意味です。
比べてみよう
Hold the bottle in one hand and pull off the top with the other.
When I passed my exams, my father held to his promise and gave me a new bicycle.
何が違うでしょう？
After the new agreement was signed between Israel and Palestine, many wondered if both sides would hold it.
A man suddenly ran into the bank. He was wearing a mask and he was holding to a gun.
My parents taught me the importance of holding my word.