Kenneth S. Wuest writes the following in regard to the Greek words translated "whosoever believes":
"'whoever believes' = 'pas ho pisteuon' = relative pronoun with a participle verb functioning as a noun, lit. 'everyone who is believing'...Contrary to objectors who insist that Jn 3:16 stipulates everyone who maintains a constant state of believing as result of the phrase 'whoever believes' = 'pas ho pisteuon', the form of the verb to believe is not a present tense form but it is actually a nominative, singular, masculine, present active participle, i.e., a participle acting as a noun indicating 'one who believes' [in Christ as Savior], i.e., a believer. The participle acting as a noun does not require a perfection of continuous action such as continuous believing in order for an individual to be qualified as a believer" (Wuest, Wuest's Word Studies, Vol. 3, [Eerdmans Publishing Co, 1992], p. 67).