What separates chalk art from other mediums is that it is built entirely around communicating the gospel. It focuses the artist on capturing an aspect of God's truth in his picture, and teaches him to use the communicating power of art to promote Biblical precepts. I am not saying that all art, in order to be godly, must be evangelistic. Art can and should communicate about the totality of life and truth. What a medium specifically devoted to evangelism demonstrates is the communicative ability and purpose of art.
Communication is thus the second half of a Christian philosophy of art.
That includes the artist, whose work, representing the character of God displayed in the created order, is a declaration of praise to Him. A Christian philosophy of art will view art as depiction rather than expression. It will see art as framing an aspect of God's creation rather than creating the artist's own reality. The believer recognizes that his art is an imitation of God's creation, an attempt to capture a piece of His handiwork in the art form. Expressional art works to deny the objectivity of reality and any order outside itself.