In this post, we will have some more clarifying statements as to what this phrase further means. To get the Scriptural context why this blog agrees with the ideas embedded in this phrase, you can find the justification in this post here.
Aside from 2 Thes 2:13-14
13 But we are [a]bound to give thanks to God always for you, brethren beloved by the Lord, because God from the beginning chose you for salvation through [b]sanctification by the Spirit and belief in the truth
We have also 1 Peter 1:2
elect according to the foreknowledge of God the Father, in sanctification of the Spirit, for obedience and sprinkling of the blood of Jesus Christ:
We have a curious phrase here which is both used by St Peter and St Paul in their writings - through sanctification of/by the Spirit. What could this mean? I suggest that to be sanctified in the Spirit is to have faith in Christ for the forgiveness of sins - John 15:26 says He is the spirit of truth and Jesus says sanctification is by God's Truth - the Word - John 17:17 and faith only comes through the word of Christ ie Law and Gospel.
Intuitu Fidei (IF) stand for in view of faith. This is a quick thumb slogan which sometimes is bound to be misunderstood. This position says God elects us in view of faith. Some Arminians think that this means we are elected for the sake of faith ( faith per se or itself as a thing). This is not what Evangelical Lutherans mean, ie the Old Orthodox Lutherans. Properly speaking they actually want to say in view of Christ's merit apprehended by faith. By this they mean to say that we are not elect by virtue of faith itself, but that which faith hangs on which is the merit of Christ ie the work and person of Christ to which faith grasps. They want to say that faith is not a meritorious property in us, but it is an instrumental cause, it grasps what is promised by the Gospel in which it addresses the demands of the Law. This is the same as what happens in Justification happens in Election/Predestination.
Because Justification and Predestination are two sides of the same coin of Salvation, we cannot have the first to be by faith and the latter to be without faith, meaning without condition ie by decree or decreetal unconditional election. The two will contradict and will rob us of the comfort of the Gospel. If it happens to be illogical only because it is contrary to the whole teaching of Scripture on the subject. IF thus say that means Election in this sense is conditioned on faith in Christ. Thus this negated decreetal/unconditional election. The best passage alluded by Calvinists for this unconditional election is in Romans 9, yet the whole argument of St Paul there pertains to the people of Israel not for every individual per se. In fact we never see in Scripture Esau serving Jacob, in fact it was reverse in that Jacob prepared gifts to his brother Jacob, even referring to himself as his servant. We see Edom, the descendants of Esau indeed subservient to Israel. Clearly as given above 1 Peter 1:2 along w Romans 8:28-29, God's foreknowledge comes first prior to predestination/election. This is something that is missed in the study of this subject.
Incidentally, many out of ignorance and specially Calvinists themselves and modern Evangelicals today think that if someone opposes Calvinism, he/she must be an Arminian. Let's correct this ignorance. For example, the famous Lutheran NT Scholar and respected Exegete - R H Lenski who was definitely anti-Calvinist, is often mis-identified as Arminian, of which of course, Arminians love to own him too. Not true.
Arminianism sprouted as a reaction to Supralapsarian Calvinism of Besa roughly 1610. The Lutherans have been rejecting Calvinism much earlier than that about 1550. In fact Arminius gave a hint that he might have been influenced in his ideas by a Danish Lutheran, Niels Hemingsen. This is the reason why I often suggest that Arminius must have picked up much of the critique of Calvinism from Lutherans.
The point of IF is that election is IN Christ, or if you will the Lord Jesus is the Elect One/ the Chosen One. That is where it happens. Since no one is in Christ unless we have faith IN Him then faith is the instrument of Election as it is the same instrument for Justification.
This is best articulated by Johann Gerhard (emphasis mine).
The good pleasure of the will of God according to which election took place, does not exclude Christ. Because Christ does not become ours except through faith (in his Gospel) therefore, the consideration of faith is a constituent part of election.
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To teach that the view of faith is a constituent part of the decree of election is not Pelagianism, for the Pelagians taught that election took place according to foreseen faith as a certain merit and as a work of natural powers of freewill, in which sense our pious (Lutheran) fathers when disputing with Pelagians justly denied that election took place for the sake of faith or from faith. But we teach that faith is a gracious gift of God and not a merit but a means through which we appropriate Christ for whose sake election took place
Reference: I believe I took this from R H Lenski's part of Errors in Missouri book. Apologies for not tracking the specifics of this.