、。
Putting an idea into action is difficult.
Literal
Thought [object-を] execution [into-に] move [nominalizer-のは], difficult.
実行に移す is a set phrase 'to put into execution/practice,' literally 'to move (X) into execution.' The pattern [X]を[Y]に移す 'move X into Y' uses に to mark the destination of the movement. のは nominalizes the preceding clause and topicalizes it — '(the act of) putting an idea into action.' A short, aphoristic sentence typical of self-help or motivational writing.