A.T. Robertson Commentary Luke 8:18

"Take heed therefore how ye hear: for whosoever hath, to him shall be given; and whosoever hath not, from him shall be taken away even that which he thinketh he hath." — Luke 8:18 (ASV)

How ye hear (πως ακουετε). The manner of hearing. Mr 4:24 has "what ye hear" (τ ακουετε), the matter that is heard. Both are supremely important. Some things should not be heard at all. Some that are heard should be forgotten. Others should be treasured and practised.

For whosoever hath (Hος αν γαρ εχη). Present active subjunctive of the common verb εχω which may mean "keep on having" or "acquiring." See on Mr 4:25 for discussion.

Thinketh he hath (δοκε εχειν), or

seems to acquire or to hold . Losses in business illustrate this saying as when we see their riches take wings and fly away. So it is with hearing and heeding. Self-deception is a common complaint.