While personification and metaphor are possibilities in terms of interpreting this line from Herman Melville's 1891 poem "Art," an examination of the lines which precede it indicate that this line is part of a biblical allusion. Once the allusion is revealed, you will get your answer.

The speaker of the poem struggles with how to make the things he dreams, thinks, and imagines (what he calls "many a brave unbodied scheme") come to life. In order for him to find the correct form and "pulsed life create," the speaker remarks at "what unlike things must meet and mate." He lists many oxymorons and opposites to make his point: 

A flame to melt--a wind to freeze; 
Sad patience--joyous energies; 
Humility-yet pride and scorn; 
Instinct and study; love and hate; 
Audacity--reverence.

Obviously, turning an idea into art is an arduous and intricate process. Then he finishes with these lines:

These must mate, 
And fuse with Jacob's mystic heart 
To wrestle with the angel--Art.

In Genesis 32:24-38, we can read about a man named Jacob who wrestled with an angel.

24 And Jacob was left alone. And a man wrestled with him until the breaking of the day. 25 When the man saw that he did not prevail against Jacob, he touched his hip socket, and Jacob's hip was put out of joint as he wrestled with him. 26 Then he said, “Let me go, for the day has broken.” But Jacob said, “I will not let you go unless you bless me.” 27 And he said to him, “What is your name?” And he said, “Jacob.” 28 Then he said,“Your name shall no longer be called Jacob, but Israel, for you have striven with God and with men, and have prevailed.” 

Jacob wrestled with an angel and would not let him go until the angel blessed him. Because of this tenacity and perseverance, the angel changed his name to Israel, which means, as the passage says, he has struggled with both God and men and has prevailed.

This must be the experience of the speaker of this poem--he must, like Jacob, wrestle with his creation, his Art, until he prevails. If that is so, Art is a metaphor for angel.