The flattest verb in the sentence
The verse spends words on the scope of love and the outcome for the believer, but the central act — the giving — arrives in two syllables with no elaboration at all.
A legal document transferring a house uses more verbiage than this verse uses for what it is describing. The deed names the parties, the consideration, the date, the conditions. The verse gives none of that. It says only that God 'gave.'
Look at where the words go instead. The love is qualified — 'so loved.' The object is sweeping — 'the world.' The son is identified precisely — 'his only born Son.' The benefit is double — 'should not perish, but have eternal life.' Everything around the act is amplified.
The act itself is not. 'He gave' has no adverb, no subordinate clause, no cost accounting. What the giving involved, what form it took, what it required — the verse does not say. It states the fact and moves immediately to the result.
Compression this severe is usually deliberate. The flattest verb in the sentence is carrying the most weight.