In the OP the Scripture passage Matthew 1:21 was included. This Scripture tells us: And she shall bring forth a son, and thou shalt call his name JESUS: for he shall save his people from their sins.
I contend that in this passage his people are the Elect, chosen by GOD unto salvation before the foundation of the world. Some, notably those who hold to a doctrine of Freewillism, of one sort or another, claim that the passage is speaking of the Jews.
It should be noted that the verb shall is used in the imperative mood. [Those versed in Greek can debate if that is the proper translation.] Now did Jesus Christ save all the Jews from their sins. Obviously not unless you champion universal salvation. Therefore, the term his people cannot refer to the Jews; it can only refer to the Elect; those chosen by GOD the Father and GIVEN to Jesus Christ [John 6:65].
The point has also been made on this thread that those chosen unto salvation are regenerated or New Birthed by the Holy Spirit while they are dead in trespass and sins and then given the gift of Saving Faith [Ephesians 2:1-8]; a truth vehemently denied by those who hold the doctrine of Freewillism [of one sort or another].
I would like to address the attention of these folks to a passage of Scripture from the Apostle Paul's letter to those Saints at Phillipi:
Philippians 1:29 For unto you it is given in the behalf of Christ, not only to believe on him, but also to suffer for his sake. This Scripture clearly teaches to all but the most, can I use the term “hardened” Freewillers, that those to whom the Apostle was writing were given the ability to believe on Jesus Christ.
That old Doctrine of Gracer John Gill writes of this truth:
For unto you it is given in the behalf of Christ, &c.] For the sake of his Gospel, for the good of his interest, and the glory of his name.
not only to believe in him; for faith in Christ, which is not merely believing that he is the Christ, and all that is said of him, or all that he himself says, but is a seeing of the Son, a going to him, receiving, embracing, leaning, relying, and living upon him, as God's salvation, is a pure gift of grace; it is not in nature, nor in every man, and in whom it is, it is not of themselves, it is the gift of God; the first implantation of it, all its acts and exercise, its increase, and the performance of it at last with power, are all owing to the grace of God; and this is only given to the elect, for it is a distinguishing gift; it is given to them, and them alone, and, therefore called the faith of God's elect:
Now I know that a lot of you folks would never resort to using the writing of anyone other than Scripture to support your view point but?????????John Gill does have a way with words and he wrote all of them {something like 10 million} with a quill pen! Amazing!