The Holy Spirit has been given to us since the Day of Pentecost (Acts 2:1-4). When you are filled in the Holy Spirit, the evidence is that you'll pray in tongues (or in other words, pray in the spirit). It's the Holy Spirit who gives you the utterance as you pray (Acts 2:4). When you pray in the spirit, you are indeed praying in the perfect will of God (Romans 8:27). Sometimes we tend to pray selfish prayers, or pray from our fleshly point of view, or we are lost for words what to pray. That's where praying in the spirit comes in. Praying in the spirit also builds yourself up on your most holy faith (Jude 20) and edifies (strengthens or energizes) your spirit (1 Corinthians 14:4). When you pray in the spirit, you are also entering spiritual rest and refresh (Isaiah 28:11-12). So, if you feel like you are in a ‘plateau’ spiritually, and you just can’t seem to progress further (i.e spiritually stagnant), do take some time off from your 'busyness', and begin spending time praying in the spirit, soaking yourself in His very presence. In fact, I suggest you pray in the spirit at least an hour everyday. You'll come out refreshed, refilled, and renewed!
The bible says, 'eye has not seen, nor ear heard, nor have entered into the heart of man, the things which God has prepared for those who love Him' (1 Corinthians 2:9). The Holy Spirit wants to reveal to you the deeper things that 'eye has not seen, nor ear heard', but you need to take time to wait on Him. One way is by praying in the spirit. You'll begin to know by revelation what God has in store for you, in every area of your life. You'll be sure what's the next step you need to take in life. You’ll also be rooted and built up in Him (Colossians 2:7). You’ll not be so easily deceived by the devil, or lured by the temptations of the world, because you know His voice, the voice of the Holy Spirit. You'll recognize His voice, and you'll follow His leading. He'll guide you into all truth (John 16:13), and He'll lead you to fulfil your God-given destiny in life. All these happen when you commune with the Holy Spirit.