会…的【huì…de】

会 on its own predicts: 明天会下雨, "it'll rain tomorrow". With 的 at the end of the sentence, the prediction becomes an assurance. The speaker is sure, and wants the listener to be sure too.

Promises

With 我 as the subject, 会…的 is a promise.

The negative

不会…的 rules something out: "won't, there's no way".

会 or 会…的

Without 的 the sentence is a plain forecast. With it, the speaker is vouching for it, often to comfort someone.

Leaving out 会

Without 会, a sentence ending in 的 reads as 是…的, which asks about an event that already happened. The 会 is what points it forward.

• × 别担心，他来的 → 别担心，他会来的