Why would Luke 4:2 and Mark 1:13 says that Christ was tempted for forty days, while Matthew says the temptations do not begin until after the forty days of fasting?
The Bible cannot contradict itself. Mark and Luke will mean that the forty days belong to the temptations because Christ became very hungry during that time and this made him more susceptible to the temptations. Matthew focuses on the main part of the temptation: when Satan came to Jesus after forty days.
3 Le tentateur, s'étant approché, lui dit: Si tu es Fils de Dieu, ordonne que ces pierres deviennent des pains.