What does it mean to be led by the Spirit? In terms of particulars, that depends somewhat on which biblical passage one is examining.
Some of the context of the Spirit’s leading in Galatians 5:18 is moral. Instead of our lives being circumscribed by written laws, God writes his law in our hearts. Thus we “walk” by the Spirit (5:16), are “led” by the Spirit (5:18), and put our steps in the footsteps of the Spirit (5:25). We follow the ways that he directs for us. Those who do this aren’t “under the law,” because we fulfill the moral demands of the law anyway (5:18, 23). We have promptings or movings that go beyond conscience. (Since conscience can be misinformed [1 Tim 4:2], learning to distinguish them can be important; but the Spirit can reshape our conscience with grace and right desire [cf. the Spirit’s godly desire in Gal 5:16-17]). That we are “led by the Spirit” presumably means that, ideally, we are following the Spirit.
Yet putting our steps in the steps of the Spirit (5:25; for further explanation of this sense in 5:25, see either of my Galatians commentaries) can have broader application than this. As Jesus did whatever he saw his Father doing (John 5:19), so we learn to discern God’s heart in Christ by the Spirit and follow along. This doesn’t mean that we always hear everything perfectly (cf. 2 Kgs 4:27; 1 Cor 13:9), but we do know the pattern, the way Christ laid before us by the way of love (5:14; 6:2). Love is certainly a key fruit of the Spirit (5:22).
Similarly, in the context of Romans 8:14, being “led by the Spirit” contrasts with being ruled by fleshly passion (8:5-13). It also involves a personal experience with the Spirit, a relationship as God’s sons and daughters (8:15-16).
Paul’s primary focus in “led by the Spirit” in Gal 5 may be moral transformation, but those who understand the Spirit’s leading exclusively in these terms commit a fallacy of drawing conclusions that are too general from particular cases. The Spirit’s moral leading is a particular example belonging to a wider experience with the Spirit. Note the following:
Neh 9:19-20 (NASB): “… The pillar of cloud did not leave them by day, To guide them on their way, Nor the pillar of fire by night, to light for them the way in which they were to go. You gave Your good Spirit to instruct them …”
Ps 139:7, 10 (NASB): “Where can I go from Your Spirit? Or where can I flee from Your presence? … Even there Your hand will lead me, And Your right hand will lay hold of me”
Ps 143:10 (NASB): “Teach me to do Your will, For You are my God; Let Your good Spirit lead me on level ground.”
Isa 63:13-14 (NIV): “who led them through the depths? Like a horse in open country, they did not stumble; like cattle that go down to the plain, they were given rest by the Spirit of the LORD. This is how you guided your people to make for yourself a glorious name.”
Matt 4:1: “Then Jesus was led up into the wilderness by the Spirit for the purpose of being tested by the devil.”
Luke 4:1 (ESV): “And Jesus, full of the Holy Spirit, returned from the Jordan and was led by the Spirit in the wilderness” (cf. 4:14 [NIV} afterward: “Jesus returned to Galilee in the power of the Spirit, and news about him spread through the whole countryside”)
John 16:13 (NRSV): “When the Spirit of truth comes, he will guide you into all the truth; for he will not speak on his own, but will speak whatever he hears, and he will declare to you the things that are to come”
These passages depict a range of way that God’s Spirit leads us, probably including Spirit-directed wisdom, intuition, and even God ordering our steps beyond our own recognition. The psalmist needs protection from enemies and also (as in Paul) guidance in God’s will (Ps 143:10). God’s Spirit is everywhere and always working in the psalmist’s life (Ps 139:7-10). Some other passages (Neh 9:19-20; Isa 63:13-14) refer directly to the exodus event, where God led his people in the wilderness by the pillar of fire (e.g., Exod 13:18; Deut 8:2, 15; 29:5; Ps 78:52; 106:9; 136:16; Jer 2:6; Amos 2:10), giving them direction where to move next as needed (e.g., Neh 9:12; Ps 78:14). They had to depend completely on him.
The Spirit leading Jesus into the wilderness (Matt 4:1; Luke 4:1), and perhaps even Paul’s language of being led by the Spirit, evokes this same imagery of God’s past leading of his people in the wilderness. From Jesus’s example, we see that sometimes the Spirit even leads us into, as well as through, hardships. From John 16:13 we learn about our intimate relationship with God, the Spirit revealing to us Jesus’s heart just as Jesus came to reveal the Father’s heart (cf. 15:15). Moreover, although Acts uses different wording, there we see the Spirit guiding God’s servants in sharing Christ with others (e.g., Acts 8:29; 10:19; 16:6-7; 19:21).
What does it mean to be led by the Spirit? In terms of particulars, that depends somewhat on which biblical passage one is examining. But overall, it means depending on God’s guidance in our lives, so we walk in the paths he wants us to walk. We don’t always in every case know exactly what his leading us, but our trust is more in his ability to lead us than in our ability to hear him. We follow our best sense of his leading, and trust in him to order our steps.
As we grow in our sensitivity to the Spirit, however, there is one area where we can be sure that his presence in our life will lead us: what is truly the leading of the Spirit will guide us in ways pleasing to God, always opposed to inclinations that do not. That is, the Spirit will never contradict the moral point that God’s Spirit already revealed in Scripture; the Spirit will empower us to live according to God’s heart.