The fifth verse (42) mentions an excuse offered by those who did not participate in the Jihad because of negligence and lethargy. It was rejected as unacceptable because they did not use the ability given by Allah to pick and choose the right thing to do in His way. Therefore, the excuse of not having that ability is not valid.
Allah admonishes those who lagged behind and did not join the Prophet for the battle of Tabuk, those who asked the Prophet for permission to remain behind, falsely pretending to have legitimate reasons to do so,
(Had it been a near gain), booty right in front of them, according to Ibn `Abbas,
(and an easy journey), travel for only a short distance,
(they would have followed you.) But,
(the distance was long for them), to Ash-Sham,
(and they would swear by Allah), when you return to them,
(If we only could, we would certainly have come forth with you), had not there been a valid excuse, we would have gone out with you,
(They destroy themselves, and Allah knows that they are liars.)