Why is Enoch called 'the seventh from Adam'?

Because he is. Jude 1:14 counts through the Genesis 5 genealogy — Adam, Seth, Enosh, Kenan, Mahalalel, Jared, Enoch — and Enoch is the seventh. What makes that number matter is what happens on it: every other generation in Genesis 5 ends with 'and he died,' but Enoch's ends with 'he was not, for God took him.' The seventh bypasses the death-cycle.

Because the count is literal and the detail matters.

Jude 1:14 is the New Testament's only explicit numbered-generation statement:

προεφήτευσεν δὲ καὶ τούτοις ἕβδομος ἀπὸ Ἀδὰμ Ἑνώχ

"And Enoch, the seventh from Adam (hebdomos apo Adam), also prophesied about these..." — Jude 1:14

Jude is counting through Genesis 5. The count is direct, verse by verse:

#NameGen 5Life spanClosing formula
1Adam5:3930 years"and he died" (v.5)
2Seth5:6912"and he died" (v.8)
3Enosh5:9905"and he died" (v.11)
4Kenan5:12910"and he died" (v.14)
5Mahalalel5:15895"and he died" (v.17)
6Jared5:18962"and he died" (v.20)
7Enoch5:21–24365 years"and he was not, for God took him" (v.24)
8Methuselah5:25969"and he died" (v.27)
9Lamech5:28777"and he died" (v.31)
10Noah5:28–29950"and he died" (Gen 9:29)

Enoch is the seventh. That is the first thing.

The second thing is what the canon does with the seventh generation. Genesis 5 follows a rigid formula: "and X lived Y years, and he fathered Z, and he lived W years after, and all his days were N, va-yamot (and he died)." Every generation ends with va-yamot. Every one except Enoch. Where the formula calls for "and he died," Gen 5:24 reads:

וַיִּתְהַלֵּךְ חֲנוֹךְ אֶת־הָאֱלֹהִים וְאֵינֶנּוּ כִּי־לָקַח אֹתוֹ אֱלֹהִים

"And Enoch walked with God, and he was not, for God took him." — Genesis 5:24

Hebrews 11:5 reads the passage as the NT's canonical interpretation: "by faith Enoch was translated so that he should not see death." The seventh generation walks into God's presence without passing through death.

Why the seventh specifically? The Hebrew Bible loads the number. Creation completes in seven days (Gen 2:2–3). The Sabbath year falls every seventh (Lev 25:4). Jubilee runs on seven sabbaths of years (Lev 25:8). Jericho falls on the seventh day of marching (Jos 6:15). Naaman is cleansed on the seventh dip (2 Ki 5:14). "Seven times a day I praise you" (Psa 119:164). Revelation is built in sevens — seven churches, seven seals, seven trumpets, seven bowls. The Hebrew root שׁבע ties the number to oath-making — "to swear" is etymologically "to seven oneself." Seven is the completion-number. It names the full measure.

So when Jude emphasizes that Enoch is the seventh, he is tying the canon's completion-number to the one figure in Genesis 5 who breaks the death-formula. Enoch's position in the count is not incidental to what happens on him. The seventh generation reaches the completion the earlier generations were moving toward, and the completion looks like walking into God's presence without having to pass through the grave.

There is one sibling observation worth noting. David in 1 Chronicles 2:15 is numbered ordinally as "David the seventh" of Jesse's sons. The Hebrew phrase is David ha-shvii — using the same ordinal shvii (seventh) that Genesis 2:3 uses for the Sabbath day and that sits behind Jude's Greek hebdomos. The seventh generation from Adam walks into God's presence; the seventh of Jesse's living sons is the one YHWH chooses as Israel's king. The numbered position is part of the selection, not decorative around it.

For the full argument — including the companion pattern of eight as new-beginning (circumcision on the eighth day, Noah preserved as the eighth, the eighth-day atzeret of Booths) and how the numbered positions close the birth-order series — see the study The Seventh and the Eighth.