I think post #12 is an outstanding presentation of the basic difference in approach.
Baptism - How does one know they are saved?
It is in the attempt to peer into the things hidden and bring them into the visible is where failures in understanding of Baptism occur and, consequently, the effectiveness of the Sacrament to encourage a believer.
Our salvation fundamentally begins in the decree of God. I drew a line on the board last Wed to show how we are saved and it begins with us being promised to Christ in eternity and ends with us reigning with Him.
But we are not privvy to the entire timeline of our redemption. We are privvy only to the timeline of our existence. We are privvy only to that which is revealed to us. We have to have some point of historical contact with this eternal purpose of God or we are left in the things hidden and can only speculate about who He has elected.
Frankly, discussions about the subjects of Baptism that focus on who God has elected from all eternity fail to identify an actual subject of Baptism. It remains hidden in God's holy counsel.
This is why God has revealed the Covenant of Grace to us and has instituted His Church in both its nascent form pre- and post-Sinai and then maturely to us in the New Covenant with Christ.
Our experience of God's covenant to save us reaches us by our hearing when we hear the Gospel preached to us. We have no experience of any regeneration that may have occurred with it. We can experience our response to it and understanding of it. We can also experience the water as it is poured on us and hear the announcement of the minister. The minister announces with the authority of God that God saves all those who trust in Christ. We then hear and taste and see Word and Sacrament regularly administered to us that declare and re-affirm the same promises. We experience our affections for the things of God and how they correspond to the delights of the heart that the Scriptures say accompany those that believe upon him.
Our experiences, then, are like points on that eternal line of God's perfect redemption. We have assurance of our salvation because God has given a promise and an oath to us. He has sworn by Himself that He saves those who believe upon His Son. Because we know we trust and we heard the Promise we are most certainly "attached" to the plan from eternity and to eternity to be saved. The visible intersects the invisible in the Covenant of Grace.
Frankly, it is my estimation that discussions that say that "...well this is speaking of spirit baptism..." wrench the Covenant of Grace from its point of contact with the eternal. It places redemption back into a point completely hidden because it divorces sign from thing signified. There is now no longer any point of contact to God's eternal plan. It's not that the Presbyterian disagrees that only those that are united to Christ by evangelical faith are truly saved and such only receive the benefits of the Holy Spirit, but it's that now the sign that signifies it is said to no longer have any real reference to it because "...only the elect participate in this...."
Thus, in the end, assurance is maintained without the problems of turning signs into the thing signified or divorcing them but placing them within their proper categories. As Bruce noted, the visible, fallible Church has, by the foolishness of Words preached, the visible role in proclaiming the Gospel in time and space. This same visible, fallible Church has the authority to ministerially declare the Promise of a God who has backed up the same Promise with an Oath so that by two unchangeable things we can be utterly convinced that the Promise will be true of those it speaks of. We hear the Word and respond and believe. We feel the Water and taste the Bread and Wine and they connect us in time and space to the eternal plan of God. Abraham never saw a great nation but he had the sure hope that everything promised to him would come to pass by a sign placed in His flesh. We have the same assurance.