'Futile' in the Bible

and again, “The Lord knows the thoughts of the [humanly] wise, that they are useless.”

and if Christ has not been raised, your faith is worthless and powerless [mere delusion]; you are still in your sins [and under the control and penalty of sin].

Therefore, my beloved brothers and sisters, be steadfast, immovable, always excelling in the work of the Lord [always doing your best and doing more than is needed], being continually aware that your labor [even to the point of exhaustion] in the Lord is not futile nor wasted [it is never without purpose].