Half a shekel - Each of the Israelites was ordered to give as a ransom for his soul (i.e., for his life) half a shekel, according to the shekel of the sanctuary. From this we may learn,

1. That the life of every man was considered as being forfeited to Divine justice.

2. That the redemption money given, which was doubtless used in the service of the sanctuary, was ultimately devoted to the use and profit of those who gave it.

3. That the standard by which the value of coin was ascertained, was kept in the sanctuary; for this appears to be the meaning of the words, after the shekel of the sanctuary.

4. The shekel is here said to be twenty gerahs. A gerah, according to Maimonides, weighed sixteen barleycorns, a shekel three hundred and twenty of pure silver. The shekel is generally considered to be equal in value to three shillings English; the redemption money, therefore, must be about one shilling and sixpence.

5. The rich were not to give more, the poor not to give less; to signify that all souls were equally precious in the sight of God, and that no difference of outward circumstances could affect the state of the soul; all had sinned, and all must be redeemed by the same price.

6. This atonement must be made that there might be no plague among them, intimating that a plague or curse from God must light on those souls for whom the atonement was not made.

7. This was to be a memorial unto the children of Israel, Exodus 30:16, to bring to their remembrance their past deliverance, and to keep in view their future redemption.

8. St. Peter seems to allude to this, and to intimate that this mode of atonement was ineffectual in itself, and only pointed out the great sacrifice which, in the fullness of time, should be made for the sin of the world. "Ye know," says he, "that ye were not redeemed with corruptible things, as silver and gold, from your vain conversation received by tradition from your fathers; but with the precious blood of Christ, as of a lamb without blemish and without spot: who verily was foreordained before the foundation of the world," etc.; 1 Peter 1:18, 1 Peter 1:19, 1 Peter 1:20.

9. Therefore all these things seem to refer to Christ alone, and to the atonement made by his blood; and upon him who is not interested in this atonement, God's plagues must be expected to fall.

Reader, acquaint now thyself with God and be at peace, and thereby good shall come unto thee.

a shekel is

Leviticus 27:25 And all your estimations shall be according to the shekel of the sanctuary: twenty gerahs shall be the shekel.

Numbers 3:47 You shall even take five shekels apiece by the poll, after the shekel of the sanctuary shall you take them...

Ezekiel 45:12 And the shekel shall be twenty gerahs: twenty shekels, five and twenty shekels, fifteen shekels, shall be your maneh.

an half shekel

Exodus 38:26 A bekah for every man, that is, half a shekel, after the shekel of the sanctuary, for every one that went to be numbered...

Matthew 27:24 When Pilate saw that he could prevail nothing, but that rather a tumult was made, he took water...

"Whereby we Cry, Abba, Father. "
Rom. viii. 15.--"Whereby we cry, Abba, Father." As there is a light of grace in bestowing such incomparably high dignities and excellent gifts on poor sinners, such as, to make them the sons of God who were the children of the devil, and heirs of a kingdom who were heirs of wrath; so there is a depth of wisdom in the Lord's allowance and manner of dispensing his love and grace in this life. For though the love be wonderful, that we should be called the sons of God; yet, as that apostle speaks, …
Hugh Binning—The Works of the Rev. Hugh Binning

Prayer
But I give myself unto prayer.' Psa 109: 4. I shall not here expatiate upon prayer, as it will be considered more fully in the Lord's prayer. It is one thing to pray, and another thing to be given to prayer: he who prays frequently, is said to be given to prayer; as he who often distributes alms, is said to be given to charity. Prayer is a glorious ordinance, it is the soul's trading with heaven. God comes down to us by his Spirit, and we go up to him by prayer. What is prayer? It is an offering …
Thomas Watson—The Ten Commandments

Exodus
The book of Exodus--so named in the Greek version from the march of Israel out of Egypt--opens upon a scene of oppression very different from the prosperity and triumph in which Genesis had closed. Israel is being cruelly crushed by the new dynasty which has arisen in Egypt (i.) and the story of the book is the story of her redemption. Ultimately it is Israel's God that is her redeemer, but He operates largely by human means; and the first step is the preparation of a deliverer, Moses, whose parentage, …
John Edgar McFadyen—Introduction to the Old Testament