Albert Barnes Commentary Psalms 138:3

"In the day that I called thou answeredst me, Thou didst encourage me with strength in my soul." — Psalms 138:3 (ASV)

In the day when I cried - Referring to some former period of his life when he was in trouble.

You answered me - In the very day when I called, you gave me the answer: that is, immediately.

And strengthened me with strength in my soul - literally, “You emboldened - or, made me courageous with strength.” You enabled me to meet danger, and to overcome fear. It would seem probable that this was on some occasion when he was in danger from his enemies.