John 6:14-15 sheds some much needed light on the parallel passage in John 2:23-25. When the diligent student of God's Word (2 Tim. 2:15) compares Scripture with Scripture ("The Analogy of Faith" principle of Bible interpretation), it becomes clear that those who believed in Christ in John 2:23 were zealous to make Him king! Such zeal is even more likely in 2:23 in view of the fact that Jesus was in Jerusalem itself, the center of the Jewish religion; the people being therefore all the more zealous for a Jewish king "from among you, from your countrymen" (Deut. 18:15) to free them from the overbearing yoke of Rome. Commenting on John 2:24, Matthew Henry explains it well when he says: "These in Jerusalem perhaps had their expectations of the temporal reign of the Messiah more raised than others, and, in that expectation, would be ready to give some bold strokes at the government if Christ would have committed himself to them and put himself at the head of them; but he would not, for his kingdom is not of this world."[2]
And in reference to John 6:1-15, for those who may think there's no possible way that these people are saved, John's Gospel actually indicates otherwise! Commenting on Jn. 6:12-15, C. K. Barrett writes the following:
"12, 13. The gathering up of the left-over fragments, again, may reflect only a characteristically Jewish respect for food; but the word used, and also the word for 'be lost', are Johannine words used for the gathering and perishing of men (see e.g. 11:52, 17:12), and it is possible that Jn means to represent this gathering symbolically.
The onlookers draw from the miracle the conclusion that Jesus is the Messiah. This belief is plainly visible in the attempt to make him a king (15), and is probably expressed also in the words, 'This is indeed the prophet' (14), 'prophet' being understood as a designation of the Messiah (cf. Dt. 18:15; and contrast 1:21, where 'the prophet' is not the Messiah). But Jesus' kingdom is not 'of this world' (18:36), and he cannot submit to be made a king by men. He withdraws to the hills (15); yet the thought of Messiahship lies in the background of the great discourse of 22-59."[3]
Barrent summarizes by saying, "It seems not impossible that John is here speaking symbolically of the gathering of Christian disciples, with special reference to the eucharist, and of the will of Christ to preserve them from all destruction (17.12; on apollunai see 3.16)."[4]
What Barrett insightfully points out is that when Jesus says, "Gather up the fragments that remain, so that nothing is lost" (Jn. 6:12, NKJV), this is likely Johannine symbolism: symbolic of Jesus gathering people into His kingdom (cf. Jn. 11:52) in order that none of them perish (cf. Jn. 3:16, 17:12, 18:9). This symbolism would seem quite strange if none of those in the crowd were saved!
The Free Grace view of John 2:23-25 is consistent with the parallel passage in 6:1-15: in both passages John describes people who have believed in Christ as the promised Messiah! Their misguided zeal "to make Him king" (6:15) is not evidence of lack of salvation; rather, their zeal can be compared to Peter's impetuous action of cutting off the ear of the high priest's servant (see Jn. 18:10). Like Peter, the crowd in John 6:14-15 had zeal, but it was not according to God's plan.
References:
[1] Note that even Wayne Grudem rejects the standard view in that he says: "It seems to me that there is room for disagreement over the meaning of 'many believed in his name' in John 2:23, but I would take it to refer to genuine trust in Christ, because believing 'in his name' is believing in him, in biblical usage [cf. Jn. 1:12; 3:18; 20:31]." (Grudem, "Free Grace" Theology: 5 Ways It Diminishes the Gospel, p. 110, footnote 14.)
[2] Matthew Henry Bible Commentary (complete), see commentary on John 2:23-25, www.christianity.com/bible/commentary/mh/john/2 (accessed April 29, 2023).
[3] C. K. Barrett, Matthew Black, General Editor and New Testament Editor, Peake's Commentary on the Bible (Nashville: Thomas Nelson Publishers, 1962), pp. 851-852, emphasis his.
[4] C. K. Barrett, The Gospel According to St John (London: SPCK, 1962), p. 231.