Despite all these incredible but real experiences of Israel with the Lord, many Israelites died for sin in the wilderness and got lost forever in hell fire (1Cor. 10:5, 8-10). Not only did they die for sin and in sin, they died prematurely too, seeing that the decision to cut them off was a later one (cons. Ex. 3:7-8; 6:2-8; Num. 14:11-12,20-23).
They were cut-off for (i) lusting after evil things (1Cor. 10:6; Num. 11:4-15; Ps. 106:14), (ii) idolatry (1Cor. 10:7; Ex. 32:1), (iii) fornication (1Cor. 10:8; Num. 25:1-9), (iv) tempting the Lord (1Cor. 10:9), through murmuring (Ex. 17:7; Heb. 4:1-11), rebellion (Num. 14:22; 21:1-9), provoking Him (Ps. 78:17-18; 56), backsliding (Ps. 78:41,56), hardening the heart (Ps. 95:8-9), lust and sin (Ps. 106:14). They were cut off also because of murmuring (1Cor. 10:10).
The above case-study of the Israelites that perished despite seeing God face-to-face (as it were) is a confirmation to us that, despite whatever experiences like being born-again, being sanctified and baptized in the Holy Spirit, being dynamic preachers or workers in the house of God, manifesting the gifts of the Spirit, whosoever returns to sin and remains there can be cut-off and sent to hell fire (cons. Gen. 19:15-26; Lk. 17:32; 1Cor. 10:6,11). And it is easy to return to sin if one does not take heed, no matter where one has reached or the experiences one had had.
Now, the sins for which these Israelites perished are still prevalent even in divers forms and in these very evil last days in particular. So then, he that thinketh he standeth must take heed, lest he falls (1Cor. 10:12). This means, he that behaves as though he has reached heaven already and has no more need for examining himself should realize that there are yet chances of being lost forever in hell, if care is not taken.