AT Robertson had not problem that in Matthew 26:28 the Greek is "FOR the remission of sins". Yet when he got to Acts 2:38 with the same exact phrase "for remission of sins in both Greek and English" he is no longer sure what "eis" means.
AT Robertson doesn't sound unsure to me. In regards to Matthew 26:28, he states - The act is symbolized by the ordinance. Cf. the purpose of Christ expressed in Hebrews 20:28. There anti and here peri. Unto remission of sins (ei apesin amartiwn). This clause is in Matthew alone but it is not to be restricted for that reason. It is the truth. This passage answers all the modern sentimentalism that finds in the teaching of Jesus only pious ethical remarks or eschatological dreamings.
He had the definite conception of his death on the cross as the basis of forgiveness of sin. The purpose of the shedding of his blood of the New Covenant was precisely to remove (forgive) sins.
Matthew 26:28 Commentary - Robertson's Word Pictures of the New Testament
In regards to Matthew 26:26-28, Jesus said, "This is my body when He took the bread." When He took the cup, He said, "This is my blood." Of course, His body was still His body and His blood was still in His body. He was attributing the reality to the emblem, yet the emblem is not the reality. When a believer is water baptized, sins are not washed away literally, but ceremonially, pointing to the death of Christ by which sins are actually washed away. Since it's not possible for an external ordinance to do an internal work on the heart, baptism can not do these things in a literal sense, yet it represents the remission of sins by the death of Christ, which was the real remission (Matthew 26:28; Hebrews 9:22-28). Christ put away sins by the sacrifice of Himself. In experience, the remission of sins comes to us through faith in Christ (Acts 26:18; Romans 3:24-26) and "remission of sins" has three applications: Literally, by the sacrificial death of Christ - Matthew 26:28, experientially, by faith in Christ - Acts 10:43; 26:18 and ceremonially, by water baptism - Acts 2:38; 22:16.
The reason he is no longer sure that eis means "for" is because Acts 2:38 as written by Luke makes baptism necessary in order to being saved. This does not fit Robertson theology therefore his attempt to change Acts 2:38 is NOT based upon the Greek language or grammar but His personal theology. He admits such when he wrote." One will decide the use here according as he believes that baptism is essential to the remission of sins or not." He did exactly this in letting his personal theology override inspiration.
Just because Robertson said that "one will decide the use here according as he believes that baptism is essential to the remission of sins or not" doesn't mean that he was confused or uncertain. Robertson understands that scripture must harmonize with scripture, but you don't seem to care that your biased interpretation of Acts 2:38 is in contradiction to other passages of scripture, so it's you who lets his personal theology override inspiration. The only logical conclusion
when properly harmonizing scripture with scripture is that faith in Jesus Christ "implied in genuine repentance" (rather than water baptism) brings the remission of sins and the gift of the Holy Spirit (Luke 24:47; Acts 2:38; 3:19; 5:31; 10:43-47; 11:17,18; 15:8,9; 16:31; 26:18). *Perfect Harmony* :)
Elsewhere, AT Robertson said - Change of number from plural to singular and of person from second to third. This change marks a break in the thought here that the English translation does not preserve. The first thing to do is make a radical and complete change of heart and life. Then let each one be baptized after this change has taken place, and the act of baptism be performed “in the name of Jesus Christ” (εν τωι ονοματι Ιησου Χριστου — en tōi onomati Iēsou Christou).
So I understand Peter to be urging baptism on each of them who had already turned (repented) and for it to be done in the name of Jesus Christ on the basis of the forgiveness of sins which they had already received.”
Greek scholar E Calvin Beisner said something similar - In short, the most precise English translation of the relevant clauses, arranging them to reflect the switches in person and number of the verbs, would be, “You (plural) repent for the forgiveness of your (plural) sins, and let each one (singular) of you be baptized (singular)….” Or, to adopt our Southern dialect again, “Y’all repent for the forgiveness of y’all’s sins, and let each one of you be baptized….”
When I showed this translation to the late Julius Mantey, one of the foremost Greek grammarians of the twentieth century and co-author of A Manual Grammar of the Greek New Testament (originally published in 1927), he approved and even signed his name next to it in the margin of my Greek New Testament. *These arguments, lexical and grammatical, stand independently. Even if one rejects both lexical meanings of for, he still must face the grammatical argument, and even if he rejects the grammatical conclusion, he still must face the lexical argument.
Does Acts 2:38 prove baptismal remission? No, it doesn’t even support it as part of a cumulative case. — E. Calvin Beisner
Greek scholar Daniel Wallace explains in Greek Grammar Beyond the Basics: It is possible that to a first-century Jewish audience (as well as to Peter), the idea of baptism might incorporate both the spiritual reality and the physical symbol (although only the reality remits sins). In other words, when one spoke of baptism, he usually meant both ideas—the reality and the ritual. Peter is shown to make the strong connection between these two in chapters 10 and 11. In 11:15-16 he recounts the conversion of Cornelius and friends, pointing out that at the point of their conversion they were baptized by the Holy Spirit. After he had seen this, he declared, “Surely no one can refuse the water for these to be baptized who have received the Holy Spirit…” (10:47). The point seems to be that if they have had the internal testimony of the Holy Spirit via spiritual baptism, there ought to be a public testimony/acknowledgment via water baptism as well. This may not only explain Acts 2:38 (that Peter spoke of both reality and picture, though only the reality removes sins), but also why the NT speaks of only baptized believers (as far as we can tell):
Water baptism is not a cause of salvation, but a picture; and as such it serves both as a public acknowledgment (by those present) and a public confession (by the convert) that one has been Spirit baptized.
*So neither AT Robertson, E Calvin Beisner or Daniel Wallace agree that water baptism is what obtains the remission of sins.
Robertson does the same thing with Tts 3:5. In order to get around the necessity of water baptism he allows his personal theology to trump inspiration.
Are you really that brain washed?

I don't see Robertson trying to get around anything. I just see you continuing to confuse the symbol with the reality, which continues to trip you up and keep you trusting in works for salvation.
Tts 3:5 as in Rom 6 both speak of a literal water baptism, a laver of water, a baptismal font where a literal "burial" takes place from which one is "raised up from" (Romans 6:4).
I like the way Robertson points out that
it is a tragedy that Paul's majestic picture here has been so blurred by controversy that some refuse to see it. It should be said also that a symbol is not the reality, but the picture of the reality. :)
Romans 6:4 Commentary - Robertson's Word Pictures of the New Testament
After this literal burial and resurrection THEN one walks in newness of life (born again). Hence baptism is for, unto securing salvation and not 'because' one is already walking in newness of life.
You are dead wrong and continue to confuse the symbol/picture with the reality and there is a reason for that. The natural man can only understand natural water.
Nothing figurative in the contexts at all...... literal laver of water in which a literal burial and resurrection takes place.
False. Are you going to tell me next that when Jesus said, "this is my body," (Matthew 26:26) that He meant it was literally His body? Roman Catholics believe it and make the same mistake you do by also confusing figurative and literal passages of scripture and the end result is salvation by works.
Robertson allowing his bias to supercede inspiration provides not proof for your position at all. You continue to try and makes things in various verses figurative in an order to get around the obvious water baptism in those verses.
It's actually you who allows their bias to supersede inspiration and you wouldn't know proof if it bit you on the nose. I see that your indoctrination into Campbellism runs very deep. There are multiple passages of scripture which make it clear that man is saved through belief/faith "apart from additions or modifications" (Luke 7:50; 8:12; John 1:12; 3:15,16,18; 5:24; 6:29,40,47; 11:25,26; Acts 10:43; 11:17; 13:39; 15:9; 16:31; Romans 1:16; 3:22-28; 4:2-6; 5:1; 1 Corinthians 1:21; Galatians 2:16; Ephesians 2:8,9; Philippians 3:9; 2 Timothy 3:15; 1 John 5:13 etc..). Salvation is through faith in the Savior God and not the water god. *Let me know when you are ready to repent and believe the gospel.