71 Another question which it is also usual to put is this: How comes it that Matthew and Luke have stated that the Lord said to His disciples that they were not to take a staff with them, whereas Mark puts the matter in this way: “And He commanded them that they should take nothing for their journey, save a staff only;” and proceeds further in this strain, “no scrip, no bread, no money in their purse:” thereby making it quite evident that his narrative belongs to the same place and circumstances with which the narratives of those others deal who have mentioned that the staff was not to be taken?
Now this question admits of being solved on the principle of understanding that the staff which, according to Mark, was to be taken, bears one sense, and that the staff which, according to Matthew and Luke, was not to be taken with them, is to be interpreted in a different sense; just in the same way as we find the term “temptation” used in one meaning, when it is said, “God tempts no man,” and in a different meaning where it is said, “The Lord your God tempts [proves] you, to know whether ye love Him.” For in the former case the temptation of seduction is intended; but in the latter the temptation of probation.
Another parallel occurs in the case of the term “judgment,” which must be taken in one way, where it is said, “They that have done good unto the resurrection of life, and they that have done evil unto the resurrection of judgment;” and in another way, where it is said, “Judge me, O God, and discern my cause, in respect of an ungodly nation.” For the former refers to the judgment of damnation, and the latter to the judgment of discrimination.
Source: The Harmony of the Gospels (New Advent)