At theological college we were reminded of this saying by Spurgeon himself: "As iron sharpens iron, so one person to another". Spurgeon was highlighting how we can help each other improve and become more Christ-like in our understanding of God, Jesus and the work of the Spirit. Spurgeon didn't make this up - he was actually quoting Proverbs chapter 27 verse 17.
My experience at college and elsewhere is that this proverb is exactly right: the banter, the discussion, the debate with fellow students helped make me clearer and sharper in my own understanding. The proverb is based on a reality: take a knife and a sharpening rod or other piece of metal, scrape them together and you will sharpen the knife. So take your life, rub it up against another believer, someone willing to challenge you, debate with you, as well as affirm you and pray for you - and you will develop and grow in your faith.
This is a key principle that should underlie our prayer partnerships and triplets. For that to be most effective you need to covenant together - agreeing to be there for each other. P. Brain in his book 'Going the Distance' expands out for us what this will look like. It will mean committing to affirm each other: so you decide that you will always love the other person, even if they offend you or do something bad. That doesn't mean that you have to always agree or accept the thing they say or do. You can point out their failings, yet you will still love them.
It also means being available: that is hard - because our time is pressured and limited. It will require allocating time and energy for your relationship, to be there for the person. Remember that iron cannot sharpen iron if there is no proximity. The two pieces have to touch and rub together!.
It will require commitment to pray for each other: not just responding to their requests and hardships, but praying pro-actively for them. The prayer relationship will require you to be open: to share your struggles, the bad as well as the good, admitting what you are thinking and where you are hurting, even where you are messing up.
That also requires honesty: the flip-side of the open sharing is to call out where you see the other is messing up, or where you disagree (but remember you continue to love!). Add to this being sensitive: with the hard stuff try your utmost to find phrasing that calls out in a spirit of affirmation, and with it try to listen to see what the underlying feelings are. Of course this also requires you to be confidential. This is crucial, you must guard what is shared.
Finally be accountable: give permission to the other to call you out, to challenge and to sharpen. Remember in Kingdom of God ministry there are to be no lone-rangers. All of us are capable of messing up, going askew, falling to old habits - the guard-rail against this is accountability. For myself as a leader I try to keep a high level of accountability to my spouse, and also to my co-elder and the leadership team - giving invitation and permission for them to counter my thinking or intended actions.
The whole purpose of this ongoing sharpening process is that together we might grow to be more Christ-like. When Paul writes to the Ephesian Christians he calls them to a greater Christian maturity in chapter 4 onwards. For example in 4:24 he writes of putting on the new self, to be 'Godlike in righteousness and holiness'. In 5:2 he writes that as a follower of Jesus, someone taking their cue and example from the life of Jesus, aim to be Christlike in 'self-giving and love'.
So we have a choice of how we live: 5:15 - 18 says don't be unwise but wise, not missing but making the most of opportunities, not being foolish but getting a good handle on God's way of living. This comes to a climax in v18 with "Don't be drunk on wine, but be filled with the Spirit". This maturity comes by learning together, sharpening one another, sharing the walk.
This can take place in the two or three of a partnership or triplet. It can also take place in the micro meet-ups we are advocating at this time. When you come together you could just chat. You could discuss the recent teaching, share and pray for each other. And you can go further and open your lives out to each other in the presence of Christ, inviting His presence to be at work among you. It doesn't have to be complicated, but coming together, sharing, and learning to practice the presence of God together opens the way for the Spirit to speak among you: key parts of the process of sharpening each other, to grow stronger and mature in Christ.