Translation:

14. When We (first) sent to them two apostles they rejected them: but We strengthened them with a third: they said "Truly we have been sent on a mission to you."

Notes (Tafseer)

3958. Allah sends His messengers or teachers of Truth by ones and twos, and where the opposition is great and He considers it necessary, he supports them with others. Their mission is divine, but they do not claim to be more than men. This is used by the unjust and the ungodly as if it were a reproach, whereas it should commend them to men, for mankind is glorified by such commission and by Allah's Self-revelation. The Message is clearly expressed in human language, but because it exposes all evil, men think it unlucky, as it checks their selfishness. It is often the poorest and most despised of mankind, from the outskirts or "farthest parts of the City", that accept the Message and are willing to work and die for it. The stiff-necked resist and accomplish their own destruction.