Albert Barnes Commentary Mark 8:24

"And he looked up, and said, I see men; for I behold [them] as trees, walking." — Mark 8:24 (ASV)

I see men as trees, walking. I see men walking; but see them so indistinctly, that but for their motion I could not distinguish them from trees. I cannot distinctly see their shapes and features.

Probably, our Lord did not at once restore him fully to sight, that He might strengthen his faith. Seeing that Jesus had partially restored him, it was evidence that He could wholly restore him, and it led him to exercise faith anew in Him, and to feel more strikingly his dependence on Him.