This passage occurs in the RCL for Holy Trinity Sunday, Year C, most recently May 2016.
Summary: This is not my favorite Holy Trinity passage; in fact, I think one needs to be really careful not to use this passage counter-productively. The use of the word paraclete (παρακλητος), often translated as advocate, suggests our need for a lawyer before our heavenly judge. While a legal metaphor of salvation may make sense in other contexts, let us be perfectly clear: In John's Gospel Jesus is not describing the Holy Spirit as our defense attorney before God the Father as judge.
Rather, Jesus presents the Holy Spirit as the abiding and living presence of God for the believers, particularly the whole community as they encounter and are challenged by the world. The Holy Spirit will continue the work of Jesus through the disciples. To put it another way, the Holy Spirit will make us holy, making us alive in Jesus Christ, both individually but also collectively. This is the work of the third person of the Trinity: to bring us into the life of God.
παρακλητος (paraclete, 15.26 and throughout John 15 and 16) The word parakletos for the Holy Spirit is a tough one to crack! The noun literally means "one called along side of." Originally it meant a "legal assistant." Hence the affinity for the term advocate.
Yet, the whole field of words related to parakletos pushes against a cold, judicial term, especially in terms of our relationship with God.
14.16 The parakletos is a gift from God
14.17 The parakletos will be with us, even abide in us forever
14.26 The parakletos will teach you and cause you to remember the words of Jesus
15.26 The parakletos will witness about Jesus
16.8 The parakletos will prove the world concerning sin, righteousness and judgment.
16.13 The parakletos will guide you on the way
16.13 The parakletos will listen to the Father and Son
16.14 The parakletos will glorify Jesus
16.14 The parakletos will make Jesus known
Interestingly, the Vulgate does not even use the term advocate to translate parakletos, instead transliterating the word "paracletus." In fact, the Latin does translate the word "parakletos" from the Greek into the Latin "advocatum" once, and this is from 1 John 2.1, where the sense is different. Indeed, here the idea is Jesus interceding for us against the judge of the Father concerning our sins; in John's Gospel the idea of the parakletos has nothing to do with a legal metaphor before God the Father, but the enabler of Christian before the world of unbelievers.
Furthermore, a look at the verb παρακαλεω, the related verb for the noun παρακλητος, really brings home that this word (really word field) is not primarily about legal matters:
Isaiah 40.1 "Comfort, comfort my people, says your God."
Psalm 23 "Your rod and staff, they comfort me."
Proverbs 8:4 "To you, O people, I call and my cry is to all that live."
2 Corinthians 1:3-4 "Blessed be the God and Father of our Lord Jesus Christ, the Father of mercies and the God of all consolation, who consoles us in all our affliction, so that we may be able to console those who are in any affliction with the consolation with which we ourselves are consoled by God."
αληθεια (truth, 16.13). The Gospel of John uses the word truth a number of times. Jesus is full of truth (1.14 and 1.17) and the truth shall set you free (8.32) but what is the truth? The best I can tell, John's Gospel asserts few things as "truth". In fact, little if anything is actually specifically stated as true, but if you do some work around times when "truth" is being debated, you can conclude a few things:
The truth is: The Word of God (1.14)
The truth is: Anyone who sins is a slave to sin (8.34); the consequence of sin is death (8.24)
The truth is: By believing in Jesus, we have life (8.24)
The truth is: Jesus and the Father are one (8.26)
The truth is: Followers of Jesus hear his voice (18.37) and walk in the light (8.12)
The truth is: Jesus is King (18.37)
To put it another way, it turns out that only some really essential things are declared/implied as truth in the Gospel of John.
οδηγεω (guide, 16.13) The verb here for "guide" is "hodege-oo" which means "hodos+ag-oo"=lead on the way; the verb is used in describing Philip's interaction with the Eunuch, where the Eunuch invites Phillip to show him the way of understanding Scripture.