While a proponent of the perseverance of the saints/eternal security, Thomas Hewitt, when commenting on Heb 6:4, noted that John Calvin and John Owen were wrong in their understanding of “tasted of the heavenly gift”:
Both Calvin
and Owen reject the idea that tasted of the heavenly gift means ‘experienced’
but in the light of ii. 9 and taking into account Psalm xxxiv. 8-10 (‘O taste
and see that the Lord is good’), which was most probably in the mind of the
writer, it seems that the persons so described had an actual experience of the
heavenly gift. This gift has been variously taken to mean the Holy Spirit, the
forgiveness of sins, the gift of redemption, and the gift of grace. Support for
all these can be found from other parts of Scripture, but it seems better to
refer it to Jesus Christ who more than once claimed to have come down from
heaven (cf. Jn. Iii.13, 31, 32, vi. 32, 35). Tasted of the heavenly gift
could then refer to those who, through repentance and faith, have had a
definite spiritual experience of Jesus Christ. (Thomas Hewitt, The Epistle
to the Hebrews [Tyndale New Testament Commentaries; Grand Rapids, Mich.:
Eerdmans, 1960], 106-7)