In asking the Lord to send forth labourers, we must also ask the Lord to equip them and make them effective witnesses which comes through the Holy Spirit.
Jesus commanded His disciples to tarry in Jerusalem until "ye shall be baptized with the Holy Ghost." Acts 1:4-5
In Acts 1:8 Jesus says, "ye shall receive power after that the Holy Ghost is come upon you: and ye shall be witnesses unto me...".
Pray for the Lord to fill His workers with His Spirit, equipping them with power, boldness (Acts 4:31), wisdom (Proverbs 11:30), zeal (Colossians 4:12-13), compassion (Jude 22-23) and divine insight (Jeremiah 33:3)
After asking the Lord to send forth labourers and to equip them with His Holy Spirit to witness of Him, we pray for the word of God that is to be shared with them. No one gets saved without hearing the word of God (Romans 10:14) and faith comes by hearing the word of God (Romans 10:17).
Since the word of God is necessary to convict (Acts 2:37), to free (John 8:32), and to save (1Peter 1:23) the lost, Satan vigorously opposes it with distractions (Luke 8:11-15), fortifications (2Corinthians 10:4-5) and substitutions (2Corinthians 11:34).
The Word of God is to Satan as Kryptonite is to superman -it makes him weak and defenseless. It also decimates his kingdom by freeing his captives for "ye shall know the truth and the the truth shall make you free" John 8:32. Satan does everything he can to keep people from knowing the truth.
In Mark 4:15 Jesus explains the parable of the sower, Jesus said that Satan comes immediately and steals away the word before the person can understand it. This is why it is so important that we pray for the word of God that is being shared.
First, pray that the word of God will "have free course" (2Thessalonians 3:1).
Next we pray for God's word to be glorified (2Thessalonians 3:1).
We also pray the word of God be multiplied (Acts 12:24). The laws of the harvest is: "He that soweth bountifully shall also reap bountifully." 2 Corinthians 9:6
Also, pray for God's word to prevail (Acts 19:20), and that it will be effective (Acts 14:1).
Isaiah 55:11 states,"So shall my word be that goeth forth out of my mouth; it shall not return unto me void, but it shall accomplish that which I please, and it shall prosper in the thing whereto I sent it."
Remember, The Pharisees - the most religious people of their day- wore the word of God on armbands and could quote large portions of scripture, yet they were as for from the kingdom of God as one could be. And, Satan quoted scripture to Jesus in Matthew 4:6.
It is only as the Holy Spirit quickens the word in the hearer's heart, that one can be saved. This is why we must pray for God's word to be effective in the lives of those hearing it.
Earnestly praying for the Lord to send forth labourers, and the word of God to be effective and quickened by the Holy Spirit is necessary for souls to be saved.