John Gill Commentary Psalms 78:34

"When he slew them, then they inquired after him; And they returned and sought God earnestly." — Psalms 78:34 (ASV)

When he slew them
Some of them, the spies particularly; or when he threatened to slay them, or was about to do it:

then they sought him ;
that is, those who either survived the slain, or were threatened with destruction; these sought the Lord by prayer and supplication, that he would not destroy them; the Targum is, "they repented and sought him;" see (Numbers 14:37Numbers 14:39Numbers 14:40).

and they returned ;
from their evil ways, and by repentance, at least in show and appearance:

and inquired early after God ;
but not earnestly, and with their whole hearts and spirits; the Targum is, "they prayed before God;"

which is often done, by carnal professors, in trouble; see (Isaiah 26:16) (Hosea 5:15) .