Doubt not but believing and miracles will happen

Mormon 9: 18-21, 27, 37

"And who shall say that Jesus Christ did not do many mighty miracles?"
"And if there were miracles wrought then, why has God ceased to be a God of miracles and yet be an unchangeable Being?  And behold, I say unto you he changeth not; if so he would cease to be God; and he ceaseth not to be God, and is a God of miracles."
"And the reason why he ceaseth to do miracles among the children of men is because that they dwindle in unbelief, and depart from the right way, and know not the God in whom they should trust."
"Behold, I say unto you that whoso believeth in Christ, doubting nothing, whatsoever he shall ask the Father in the name if Christ it shall be granted him; and this promise is unto all, even unto the ends of the earth."
"...hearken unto the words of the Lord, and ask the Father in the name of Jesus for what things soever ye shall stand in need.  Doubt not, but be believing, and begin as in times of old, and come unto the Lord with all your heart..."
"And may the Lord Jesus Christ grant that [your] prayers may be answered according to [your] faith;...and may he bless [you] forever, through faith on the name of Jesus Christ. Amen."