Hebrews 7:13

For he of whom these things are said belongeth to another tribe, from which no man hath given attendance at the altar. For it is evident that our Lord hath sprung out of Judah; as to which tribe Moses spake nothing concerning priests.

Here is another emphasis upon the extraordinary change involved in the establishment of the high priesthood of Christ, in that he came from a tribe hitherto absolutely excluded from any participation in such an office. The author's mention of Judah and the statement that it was "evident" Christ came from the tribe shows that the readers were familiar with the genealogy of Jesus, a genealogy stressed by Christians from the first, and doubtless also by the Pharisees, who would have used it to "prove" Christ could not be a priest! Both Matthew and Luke traced the ancestry of Jesus back through Judah; and the Christian designation of our Lord as "the Lion of the tribe of Judah" (Revelation 5:5) came from the information thus given.

Belongeth to another tribe does not give the full weight of the meaning, as a glance at the English Revised Version (1885) margin will show. The Greek has "hath partaken of" and shows that it was of Christ's initiative and volition that he was born of the tribe of Judah, a thing that could not possibly be said of a mere human being. The same thought occurs in Hebrews 2:4. As to WHY Jesus elected to be born of the tribe of Judah, it is perfectly evident that he did so because of the prophecies, notably Genesis 49:8-12.

Hath sprung out of is usually seen as an allusion to the springing up of plants, the same figure appearing in Isaiah 11:1; but it is possible that here is imagery comparing the rising of the Messiah to the rising of the sun (Malachi 4:2), or to the rising of a star (Numbers 24:17; 2 Peter 1:19). Also, the dramatic and challenging nature of his sudden appearance is indicated.