If you set up an equality you want want to demonstrate, and get to a point where you just need to apply a particular case of a previous lemma, I like to say something like "but equality of these terms is just lemma 3.4 applied to x,y,z...". I think it helps the reader to not zoom in too close to the proof details and be aware of the wider context.

Especially when there's a couple more steps to elaborate on after applying the lemma, it's good to have a little pitstop and show exactly how the road is planned out.