Why does Christ appear to have no beauty from the outside but is beautiful to those in Him?
The context contrasts outward appearance with inward revelation: from the outside, Christ has no beauty that we should behold Him; but once a person becomes involved in Christ, He is everything and beautiful. Only the believer can understand all that He is, while those outside do not see or experience that beauty.
Les explains this by using the tabernacle tent as an illustration. The outside did not reveal the beauty within; the fine twined linen was woven with blue, purple, scarlet, and the likenesses of cherubims. A person coming into the tent would not see or experience that beauty until the priests came inside. In the same way, Christ hath no beauty from the outside that we should behold Him, but once we become involved in Christ, He is everything and is beautiful. Only the believer can understand all that He is.