。
Practice is the path to mastery.
Literal
Practice [topic-は] mastery [of-の] path.
A short proverb structured as A は B (topic-comment) with the copula dropped — the default proverb shape in Japanese. 熟達 means 'mastery, proficiency,' and the literal reading 'practice is the path of mastery' captures both cause and process. Compare the more common 習うより慣れろ ('getting used to it beats being taught').