Best way to memorize opening lines?

I feel silly attempting to answer your question since you are so higher Rated than me. But, this what helped me. I bought an MCO 15 and read through the entire book playin out the moves with a board and peices. the openings that i played, i played through multiple times. as I played through the opening variations I even began to get an understanding of why in general the moves were made in a certain sequence for both sides.

I use another site's book editor and trainer because it's tree based and helps me find transpositions, but I don't like the way it either jumps to random lines making it hard to learn 1 concept at a time and when you try to do systematic study, it skips to the next branch for every line and refuses to play all the in between moves that "show you the path to the position" which wastes a lot of time and confuses me with move orders.

before I quit chess a decade ago, I used to make my own hand written trees and hide the moves with a couple pieces of paper and play everything on a literal chess board & have to reset the pieces after each attempt to learn a line. it worked, but it was very slow.

the way I think I learned better was when I turned every line of theory into a separate game, and then study each and every line, one at a time until I had it memorized for something like 15 moves. with just a FEW (50ish?) lines of theory, I had my very first opening successes as a 1400 as well as a score pushing 90% in the smith morra gambit!

i like playing through an entire line of theory, one line at a time until i get it before wandering down the next path. spaced repetition and i do not get along at all

memorizing lines sounds like the opposite of fun, is 2000+ where chess stops being enjoyable and turns into homework?

#5, yes. but it must be done if you wish to play at a higher level. the best analogy I can think of is this: T ball, little league, high school baseball, college baseball, minor leagues, and the MLB. it is the same game but at each level there exists a different understanding of the game. and you must master and apply that understanding if you wish to play on a higher level.

Thanks all for your responses! I suppose I'll have to start creating and learning opening trees, although it sounds like a tedious job. I'll start with the variations that I have the biggest issues playing against, such as Milner-Barry in French and only then move to the more complex main lines.

#5 no, chess is still enjoyable, but if you want to improve at that level it's necessary to devote an increasing amount of time to learning less enjoyable elements of the game. As a matter of fact, I knew one chessplayer who stopped playing competitively at the age of 18, when he was rated almost 2300 precisely for the reason of not being willing to devote his time to learning openings.

By understanding the logic. If you don't understand the logic, you won't be able to remember it. But after going deeper than 10moves, it would become rote memorization almost*

Wait, I just took a look at your profile. I think at your level it all comes down to looking at your files multiple times and practicing it alone on a real board. That's it there's no secret