‘For we wrestle,’ Eph. 6:12.
This is a ground of consolation to the weak Christian, who disputes against the truth of his grace, from the inward conflicts and fightings he hath with his lusts, and is ready to say like Gideon, in regard of outward enemies, ‘If God be with me, why is all this befallen me?’ Why do I find such strugglings in me, provoking me to sin, pulling me back from that which is good? Why dost [thou] ask? The answer is soon given; because thou art a wrestler, not a conqueror. Thou mistakest the state of a Christian in this life. When one is made a Christian, he is not presently called to triumph over his slain enemies, but carried into the field to meet and fight them. The state of grace is the commencing of a war against sin, not the ending of it; rather than thou shalt not have an enemy to wrestle with, God himself will come in a disguise into the field, and appear to be thine enemy. thus when Jacob was alone, a man wrestled with him until breaking of the day; and therefore set thy heart at rest if this be thy scruple. Thy soul may rather take comfort in this, that thou art a wrestler. This struggling within thee, if upon the right ground, and to the right end, doth evidence there are two nations within thee, two contrary natures, the one from earth, earthly, and the other from heaven, heavenly; yea, for thy further comfort, know [that] though thy corrupt nature be the elder, yet it shall serve the younger.
-excerpted from The Christian in Complete Armour by William Gurnall