That whosoever - This shows the fulness and freeness of the gospel. All may come and be saved.Believeth in him - Whosoever puts confidence in him as able and willing to save. All who feel that they are sinners, that they have no righteousness of their own, and are willing to look to him as their only Saviour.
Should not perish - They are in danger, by nature, of perishing - that is, of sinking down to the pains of hell; of being "punished with everlasting destruction" from the presence of the Lord and from the glory of his power, 2-Thessalonians 1:9. All who believe on Jesus shall be saved from this condemnation and be raised up to eternal life. And from this we learn:
1. that there is salvation in no other.
2. that salvation is here full and free for all who will come.
3. that it is easy. What was more easy for a poor, wounded, dying Israelite, bitten by a poisonous serpent, than to look up to a brass serpent? So with the poor, lost, dying sinner. And what more foolish than for such a wounded, dying man to refuse to look on a remedy so easy and effectual? So nothing is more foolish man for a lost and dying sinner to "refuse" to look on God's only Son, exalted on a cross to die for the sins of men, and able to save to the uttermost "all" who come to God by him.

That whosoever believeth - Bp. Pearce supposes that this verse is only the conclusion of the 16th, and that it has been inserted in this place by mistake. The words contain the reason of the subject in the following verse, and seem to break in upon our Lord's argument before he had fully stated it. The words, μη αποληται αλλα, may not perish but, are omitted by some very ancient MSS. and versions.

That whosoever believeth in him,.... Whether Jew or Gentile, a greater, or a lesser sinner, and of whatsoever state and condition, age or sex; and though ever so weak a believer, provided his faith, is of the right kind: not an historical or temporary one, a mere assent to the truth of things respecting his person, office, and work; but such a faith, by which a soul sees a glory, fulness, and suitableness in him as a Saviour; goes to him, ventures on him, commits itself to him, lays hold on him, and receives him, leans and relies upon him, and trusts in him, and lives upon him; and which is the faith of God's elect; a gift of his grace, and the operation of his Spirit; and which works by love, and is attended with the fruits of righteousness: now the end of Christ's crucifixion and death is, that such an one
should not perish; though he is in a lost and perishing condition in Adam, and by nature, and sees himself to be so, and comes to Christ as such; and though his frames and comforts are perishing, and he sometimes fears he shall be utterly lost; and though he is subject to slips and falls, and great spiritual decays; and shall perish as to the outward man by death; yet he shall never perish eternally, or be punished with everlasting destruction, as the wicked will:
but have eternal life; not by his works, but as the gift of God: and which he that truly believes; has already in the covenant of grace, in Christ his head, in faith and hope; and has the earnest and pledge of it, the Spirit of God; and the beginning of it, which is the knowledge of God in Christ; and shall hereafter possess it fully, and in person, to all eternity: even a life of perfect holiness and knowledge; a life of never ending pleasure; a life free from all the sorrows, distresses, and imperfections of this; and which will always continue.

That whosoever - He must be lifted up, that hereby he may purchase salvation for all believers: all those who look to him by faith recover spiritual health, even as all that looked at that serpent recovered bodily health.