Jesus reassured the disciples that they can know the way. But that isn't the only promise that Jesus assured the disciples in the trying times.
Jesus proclaimed that those who believe in Jesus would not only do Jesus's works but also "greater works [...] because [Jesus] go[es] to the Father" (14:12). By the way, it's important to notice that in context, "believe in Jesus" refers to the daily act of counting on Jesus to counter fear and to guide our life (as seen when Jesus told his disciples, who were already saved, to believe in Jesus). Lucas Kitchen further explains this in this article. Thus, Jesus talks about how we who count on Jesus to counter fear and to guide our life can do "greater works".
Jesus turned water to wine and raised a man from the dead -- how are we going to top that? It's heavily implied that Jesus referred to "greater works", he refers to works that impact more people. In particular, the disciples started the Church that lasted for over 1900 years and spread through multiple continents. Even today, Jesus often uses us to impact other people (some of which involves our friends receiving everlasting life upon accepting Jesus).
Additionally, Jesus promises that "whatever [the disciples] ask in [His] name, that [He] will do" (14:13-14). Now it's important to note what this means (spoiler alert -- it doesn't necessarily mean that we'll have a Ferrari if we ask Jesus). According to the Interlinear, the Greek word for "name" (Strong 3686) means "character/fame/reputation". Thus, "asking in the name of Jesus" means "asking based on the character of Jesus or what Jesus wants". In other words, our requests should reflect what Jesus does, but when we do ask in the character of Jesus, said thing we're asking for WILL happen (pun intended). Some examples of requests in Jesus's name include requests for renewed heart, transformation, and a heart to reach for others.