A.T. Robertson Commentary Hebrews 6:8

"but if it beareth thorns and thistles, it is rejected and nigh unto a curse; whose end is to be burned." — Hebrews 6:8 (ASV)

If it beareth (εκφερουσα). Present active participle of εκφερω, conditional participle. For "thorns and thistles" see Mt 7:16 for both words (ακανθας κα τριβολους). Roman soldiers scattered balls with sharp iron spikes, one of which was called tribulus, to hinder the enemy's cavalry.

Rejected (αδοκιμος). See 1 Corinthians 9:27; Romans 1:28. For καταρας εγγυς (nigh unto a curse) see Gal 3:10.

To be burned (εις καυσιν). "For burning." Common sight in clearing up ground.