'Fruitless' in the Bible

For Christ did not send me [as an apostle] to baptize, but [commissioned and empowered me] to preach the good news [of salvation]—not with clever and eloquent speech [as an orator], so that the cross of Christ would not be made ineffective [deprived of its saving power].

But by the [remarkable] grace of God I am what I am, and His grace toward me was not without effect. In fact, I worked harder than all of the apostles, though it was not I, but the grace of God [His unmerited favor and blessing which was] with me.

and if Christ has not been raised, then our preaching is vain [useless, amounting to nothing], and your faith is also vain [imaginary, unfounded, devoid of value and benefit—not based on truth].

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 dear brethren, be firm, unmovable, busily occupied at all times in the Lord's work, knowing that your toil is not fruitless in the Lord.