If you wish to be an accurate interpreter of the Scriptures, learning the languages in which the Old and New Testaments were written can be extremely valuable. With the exception of parts of the books of Ezra and Daniel, which are written in Aramaic, the rest of the Old Testament is in Hebrew and the New Testament is in Greek. A number of good resources for learning Hebrew and Greek are available online.
Denver Seminary lists some recommended Hebrew grammars and Hebrew lexicons on this page:
For learning Greek, some recommended texts are the following:
Biblical language books published from about 1960 to about 2010 can be borrowed online at archive.org. These include elementary grammars for learning the languages, research grammars and lexicons. I have made a list of some of them here: Biblical Language Books to Borrow.
Videos, Lectures and Courses:
If you wish to learn Hebrew and Greek, a number of online videos, lectures and courses are also available.
Another great resource for learning Hebrew are the communicative Hebrew videos produced by Beth and Andrew Case at https://www.youtube.com/c/AlephwithBeth/featured. Even a person who doesn’t know English well can learn basic Hebrew using these videos. The Cases have also listed many resources to aid in learning Hebrew at https://freehebrew.hismagnificence.com/resources/
One can also learn Hebrew by means of the courses and classes available at the Biblical Language Center.
Videos based on the book Beginning with New Testament Greek by Ben Merkle and Rob Plummer (see the link above), are available at https://dailydoseofgreek.com/learn-biblical-greek/.
Additional video lectures are available at: Lectures on the Basics of Biblical Greek by Dr. Mark Schuler
Luke Amadeus Ranieri has begun producing a series of Greek lessons using “comprehensible input” at Ancient Greek in Action.
William Mounce, the author of Basics of Biblical Greek Grammar (see the link above), has options for learning for learning biblical Greek at his website: https://www.billmounce.com/
Other options for learning Koine Greek include the following: