6:4 once been enlightened. That is, had the knowledge of God disclosed in the gospel message (10:26; John 1:9; 2 Cor. 4:4–6) and publicly confessed in baptism. In early Christian writings, conversion and baptism were sometimes termed “enlightenment.” The Greek word for “once” is prominent in Hebrews. It is used in connection with the once-for-all sacrifice of Christ in 10:2, 10.

tasted the heavenly gift. Some see here a reference to participation in the sacrament of the Lord’s Supper. Or the phrase could be paired with “enlightened” as a broad description of apparent conversion.

shared in the Holy Spirit. They had some experience with the gifts of the Holy Spirit, but it is not necessary to conclude that regeneration is specifically intended.