Four of the eight beatitudes are found, with some differences, in both Matthew and Luke.
The beatitudes as recorded in Matthew are:
- Blessed are the poor in spirit: for theirs is the kingdom of heaven
- They that mourn: for they will be comforted
- The meek: for they shall inherit the earth
- They which do hunger and thirst after righteousness: for they shall
- The merciful: for they shall obtain mercy
- The pure in heart: for they shall see God
- The peacemakers: for they shall be called the children of God
- They which are persecuted for righteousness' sake: for theirs is the kingdom of heaven.
The corresponding four beatitudes in Luke are different in meaning, although the words are almost the same:
- Blessed are the poor, for theirs is the kingdom of heaven
- Those who are weeping, for they will laugh
- The hungry, for they will be satisfied
- Followers of the Son of Man, for theirs is the kingdom of heaven.
A key difference between the two sets of beatitudes is that Matthew's is spiritual, consistent with the theme of the gospel as a whole, while Luke's is more concerned with problems the poor face, which is also a theme throughout Luke's Gospel. Thus, in Luke's first beatitude, "blessed are the poor," while Matthew's first beatitude says "blessed are the poor in spirit." Most New Testament scholars recognise the four beatitudes common to both Matthew and Luke as coming from the hypothetical 'Q' document (6:20-23), used by both authors as a source for sayings attributed to Jesus, and trace the remaining four back to other sources known to Matthew. When copying from Q, Luke's Gospel is usually considered closer to the original in Q, meaning that "blessed are the poor" is probably the original *.
The meaning of Matthew's "poor in spirit" has resulted in a great deal of discussion, with no consensus on how it should be understood. On the surface, it should be those who are rich in spirit who inherit the kingdom of heaven, but theologians find various innovative ways to explain the apparent contradiction. Thus, we have Williard's hypothesis that you have found lacking in objectivity.
Often these attempts at explanation overlook Matthew's use of Q as the source for the first four beatitudes. Matthew took a source that we also know from Luke and produced a very different beatitude by the addition of two words, "in spirit." Perhaps the answer is as simple as that this was a Matthean elaboration of the original wording in Q, that just did not quite work out.
(*) The Q document is a hypothetical document- i.e. no extant copy now exists, although scholars believe they can synthesise it with reasonable accuracy because of its use in the Gospels of Matthew and Luke. The standard treatment of the Q document is to give chapter and verse numbers that correspond to the equivalent passages in Luke, in recognition of Luke following the original text more closely than does Matthew. Raymond E. Brown says in An Introduction to the New Testament, page 122, "In the judgment of most, the existence of Q remains the best way of explaining the agreements between Matt and Luke in material they did not borrow from Mark." John Dominic Crossan says in The Birth of Christianity, pages 110-111, that The Q Gospel is a hypothetical document whose existence is persuasively postulated to explain the amount of non-Markan material found with similar order and content in Matthew and Luke. He adds that this postulate does not have the massive consensus that Markan priority has [that the Gospels of Matthew and Luke were substantially based on Mark], but it is certainly a major scholarly conclusion.
Even if we did not have 'Q' as a major scholarly conclusion for sayings material that does not come from Mark's Gospel, we would still need another explanation for the material, given the very strong consensus that the Gospels of Matthew and Luke were substantially based on Mark's Gospel. Uta Ranke-Heinemann says in Putting Away Childish Things, page 218, that Matthew takes over almost all Mark's material, Mark's sequence of events and, for the most part, Mark’s wording. It is incomprehensible that an eyewitness (the Apostle Matthew) would choose to depend so radically on a non-eyewitness (the author of Mark). She adds that the real author of Matthew is unknown. In that regard, it is important to note that all the New Testament gospels were originally anonymous and were only attributed to the persons whose names they now bear later in the second century.