Nephi continues his theme of sin from verse 17. It is best to read this sentence as a parallel to verse 17's
"Yea, my heart sorroweth because of my flesh; my soul grieveth because of mine iniquities."
Nephi confesses that he, although blessed of the Lord, is yet subject to temptation. He indicates that this is no rare event, but that such opportunity for sin has him "encompassed about." The opportunity to sin is on every side, and Nephi still feels the temptations. While Nephi is freely confessing to temptation, it is very likely that he is not confessing to succumbing as frequently to temptation, for his spiritual righteousness was still high enough to have received tremendous spiritual experiences, experiences that were not all in his past.