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To play baseball, you need a bat, a ball, and a glove.
Literal
Baseball [obj-を] do-[for-には] bat [and-と] ball [and-と] glove [subj-が] necessary [copula-だ].
~には here is the purposive には ('for (doing) X'), combining purpose に with topic は. ~と~と~ is the exhaustive listing と — each item in the list is separated by と, and the final one can optionally omit the と. 必要だ ('necessary') takes the needed thing as subject with が.