A.T. Robertson Commentary John 7:17

"If any man willeth to do his will, he shall know of the teaching, whether it is of God, or [whether] I speak from myself." — John 7:17 (ASV)

If any man willeth to do (εαν τις θελη ποιειν). Condition of third class with εαν and present active subjunctive θελη not used as a mere auxiliary verb for the future "will do," but with full force of θελω, to will, to wish. See the same use of θελω in 5:40 "and yet ye are not willing to come" (κα ου θελετε ελθειν).

He shall know (γνωσετα). Future middle indicative of γινωσκω. Experimental knowledge from willingness to do God's will. See this same point by Jesus in 5:46; 18:37. There must be moral harmony between man's purpose and God's will. "If there be no sympathy there can be no understanding" (Westcott). Atheists of all types have no point of contact for approach to the knowledge of Christ. This fact does not prove the non-existence of God, but simply their own isolation. They are out of tune with the Infinite. For those who love God it is also true that obedience to God's will brings richer knowledge of God. Agnostic and atheistic critics are disqualified by Jesus as witnesses to his claims.

Of God (εκ του θεου). Out of God as source.

From myself (απ' εμαυτου). Instead of from God.