Luke 14:16-24
(verse 21) Then the master of the house, being angry, said to his servant, ‘Go out quickly into the streets and lanes of the city, and bring in here the poor and the maimed and the lame and the blind.’ (NKJV)
I walked into church on a Saturday afternoon for rehearsals and as the clock ticked, just a few members showed up. The choir Director insisted that we go ahead to commence rehearsal as I heard her say, “In the house of God, there are no vacancies.” This is a true saying and worthy of all acceptance.
It will be good to lay a foundation by saying that God has called every believer into the work of the ministry. The moment you were saved, you received the responsibility to carry the gospel to others in order that they might be saved as well. You did not just receive the responsibility but you were also given the ability to carry out the task. Thus, we are called ‘able ministers’. Someone defined responsibility’ as ‘responding to ability’.
2 Corinthians 3:5-6 - Not that we are sufficient in ourselves to claim anything as coming from us, but (our sufficiency is from God, who has made us competent[ to be ministers of( a new covenant,… (ESV)
2 Corinthians 5:18-20  But all things are from God, Who through Jesus Christ reconciled us to Himself [received us into favor, brought us into harmony with Himself] and gave to us the ministry of reconciliation [that by word and deed we might aim to bring others into harmony with Him]. (Amplified Version)
1 Corinthians 9:16-17  For if I do this work of my own free will, then I have my pay (my reward); but if it is not of my own will, but is done reluctantly and under compulsion, I am [still] entrusted with a [sacred] trusteeship and commission. (Amplified Version)
As we read in the text, God is not all out looking for those who are fit and altogether correct to carry out His work, He simply requires faithfulness, those who are available.  For the purpose of this discuss, I would consider faithfulness in service to God within Christendom and not necessarily ‘the preaching of the Gospel’ although it is a common factor to both. 2 Timothy 2:2 explains this properly as Paul wanted to teach Timothy how to cast the vision. He instructed him to commit to ‘able men who shall be faithful’, No! Because the sad thing about faithful man is that, they are not always faithful. Instead, Paul instructed him to commit to ‘faithful men who also shall be able’.
And the [instructions] which you have heard from me along with many witnesses, transmit and entrust [as a deposit] to reliable and faithful men who will be competent and qualified to teach others also. (Amplified Version)
The truth of the matter is that faithfulness is the key to success of any endeavor in life, especially in the Ministry. Also, at the point where the disciples needed to replace Judas Iscariot, they had criteria and a category of people they intended to select from: men who had been with them ALL THE TIME when Jesus went in and out with them. The only requirement was FAITHFULNESS.
Acts 1:21-22  Wherefore of these men which have companied with us all the time that the Lord Jesus went in and out among us, Beginning from the baptism of John, unto that same day that he was taken up from us, must one be ordained to be a witness with us of his resurrection. (KJV)
Sometimes, looking out for faithful men may seem like an act of compromise: compromise of quality for quantity (because they may not look competent enough for the work at such point in time).  There is error in this notion because every believer has already been enabled for the work of the Ministry. All that is needed is opportunity earned by faithfulness.
Another mistake we can make is to look for faithful men who will carry on our own traditions and ideologies. We must search out faithful men and be ready to listen to whatever new ideas that they bring. Do not put them in a box where all they think is ‘this is how we have always done it’ rather than ‘this is what the Lord is saying right now.’
As far as the work of the ministry/service in His vineyard is concerned, some Christians grumble that they are not being charged with responsibilities because they have not paid the price – faithfulness. This alone will earn you opportunity even when you least expect it.  I know you are too ‘loaded’ with all that gift and talent but nobody is going to discover you until you are available.
The requirement from a steward of Christ and a Minister of God is faithfulness.
1Corinthians 4:1-2  SO THEN, let us [apostles] be looked upon as ministering servants of Christ and stewards (trustees) of the mysteries (the secret purposes) of God. Moreover, it is [essentially] required of stewards that a man should be found faithful [proving himself worthy of trust]. (Amplified Version)
Of a truth there are no vacancies in the House of God, He is quick to replace any unavailable vessel with an available one because the work must go on.
Proverbs 22:29  Do you see a man diligent and skillful in his business? He will stand before kings; he will not stand before obscure men. (Amplified Version)
Proverbs 25:13  Like the cold of snow [brought from the mountains] in the time of harvest, so is a faithful messenger to those who send him; for he refreshes the life of his masters. (Amplified Version)
Proverbs 25:19  Confidence in an unfaithful man in time of trouble is like a broken tooth, and a foot out of joint. (Amplified Version)