en_tn/mrk/11/23.md

Truly I say to you

"I tell you the truth." This phrase adds emphasis to what Jesus says next.

whoever says

"if anyone says"

if he does not doubt in his heart but believes

Here "heart" is a metonym for a person's mind or inner being. AT: "if he truly believes in his heart" or "if he does not doubt but believes" (See: rc://en/ta/man/translate/figs-metonymy)

God will do

"God will make happen"