What does "吾力足以舉三千斤" mean?

In the clause "吾力足以舉三千斤 (오력족이거삼천근)," why does 以 (이) come between 足 (족), which means "to be enough," and 擧 (거), which means "to lift"?

Some scholars explain this 以 (이) by saying that it is used with such “special” adjectives as 足 (족) and 可 (가) when 足 and 可 are followed by intransitive verbs and by transitive verbs being used in the active voice. They further explain that 以 is omitted when 足 and 可 are followed by transitive verbs being used in the passive voice. Though that may be the result of using such adjectives, I suspect the ancient Chinese were not thinking about transitive and intransitive and passive and active when they wrote their sentences, so here is my simpler theory:

When 以 (이) follows adjectives like 足 (족) and 可 (가), it is being used with its verbal meaning of “to use.” Therefore, the clause “吾力足以擧三千斤 (오력족이거삼천근)” literally translates as follows:

“My (吾) strength (力) is enough (足) to be used (以) to lift (擧) 3,000 (三千) pounds (斤).”

Whether or not my theory is correct, it seems to work, and can be used without much explanation or thought, and I think the ancient Chinese would agree. Here is my translation of a passage from the "Analects of Mencius," from which the above sentence came:

孟(맹)子(자)曰(왈), 有(유)人(인)曰(왈), 吾(오)力(력)足(족)以(이)舉(거)三(삼)千(천)斤(근), 而(이)不(부)足(족)以(이)舉(거)一(일)羽(우), 王(왕)信(신)之(지)乎(호), 可(가)知(지)一(일)羽(우)之(지)不(불)舉(거), 爲(위)不(불)用(용)力(력)也(야), 是(시)其(기)不(불)爲(위), 而(이)非(비)其(기)不(불)能(능)也(야).

Mencius (孟子) said (曰), “[Suppose] someone (有人) were to say (曰), ‘My (吾) strength (力) is enough (足以) to lift (舉) three thousand (三千) pounds (斤), but (而) is not (不) enough (足以) to lift (舉) one (一) feather (羽)’; [would] your Majesty (王) believe (信) him (之乎)? It would be obvious (可知) the one (一) feather’s (羽之) not (不) being lifted (舉) would be because (爲) [he] is not (不) using (用) [his] strength (力也). This (是) [is] his (其) not-doing (不爲), and (而) not (不) his (其) being incapable (不能).