Luke 5:5

And Simon answering said unto him, master
Or Rabbi, as the Syriac version renders it: he knew him to be the Messiah, the king of Israel, and a teacher sent from God:

we have toiled all the night, and have taken nothing;
which carries in it an objection to what Christ advised and directed to: they had been fishing that "night", which was the best time for catching fish; and they had been at it all the night, and had "laboured" hard; and were even "fatigued", and quite wearied out; and what was most discouraging of all, their labour was in vain; they had caught "nothing":

nevertheless at thy word I will let down the net;
which showed faith in Christ, and obedience to him: thus the faithful preachers of the Gospel, sometimes labour and toil in the ministry of the word a great while, with little or no success; and are discouraged from going on, and would be tempted to leave off, were it not for the commission and word of command they have received from Christ, which they dare not be disobedient to; and for the word of promise he has given them, to be with them, on which they depend.